Channel-specific micro-optics for optical arrays

ABSTRACT

A multispectral sensor array can include a combination of ranging sensor channels (e.g., LIDAR sensor channels) and ambient-light sensor channels tuned to detect ambient light having a channel-specific property (e.g., color). The sensor channels can be arranged and spaced to provide multispectral images of a field of view in which the multispectral images from different sensors are inherently aligned with each other to define an array of multispectral image pixels. Various optical elements can be provided to facilitate imaging operations. Light ranging/imaging systems incorporating multispectral sensor arrays can operate in rotating and/or static modes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the following four provisionalapplications: U.S. Application No. 62/716,900, filed Aug. 9, 2018; U.S.Application No. 62/726,810, filed Sep. 4, 2018; U.S. Application No.62/744,540, filed Oct. 11, 2018; and U.S. Application No. 62/877,778,filed Jul. 23, 2019. The disclosures of all four of these provisionalapplications are incorporated herein by reference.

This application is also related to the following four U.S. patentapplications filed of even date herewith: U.S. application Ser. No.16/534,838; U.S. application Ser. No. 16/534,885; U.S. application Ser.No. 16/534,895; and U.S. application Ser. No. 16/534,910. Thedisclosures of these four applications are incorporated herein byreference.

BACKGROUND

The present disclosure relates generally to optical imaging systems andin particular to sensor systems with multiple sensor channels tuned todifferent light characteristics or properties and that include sensorchannels usable for ranging.

Light imaging, detection and ranging (LIDAR) systems measure distance toa target by illuminating the target with a pulsed laser light andmeasuring the reflected pulses with a sensor. Time-of-flightmeasurements can then be used to make a digital 3D-representation of thetarget. LIDAR systems can be used for a variety of applications where 3Ddepth images are useful including archaeology, geography, geology,forestry, mapping, construction, medical imaging, and militaryapplications, among others. Autonomous vehicles can also use LIDAR forobstacle detection and avoidance as well as vehicle navigation.

In applications such as vehicle navigation, depth information (e.g.,distance to objects in the environment) is extremely useful but notsufficient to avoid hazards and navigate safely. It is also necessary toidentify specific objects, e.g., traffic signals, lane markings, movingobjects that may intersect the vehicle's path of travel, and so on.Accordingly, systems such as autonomous vehicles may include both aLIDAR system and another imaging system, such as a visible-light camerathat can capture ambient light, including reflected light from objectsin the environment as well as direct light from any light source thatmay be present in the environment. Each imaging system (LIDAR andvisible-light) independently provides an image containing either depthor spectral data. For some applications, it is beneficial to align thedifferent images with each other, e.g., by performing image registrationto identify the position of the same object in different images. Imageregistration can be a complex and computationally intensive task. Forinstance, different imaging systems may have different resolutionsand/or frame boundaries, and the alignment between independentlyconstructed and/or independently controlled imaging systems may beinexact.

SUMMARY

Certain embodiments of inventions described herein relate tomultispectral sensor arrays that incorporate multiple sensor channeltypes, including depth channels (e.g., LIDAR sensor channels) and one ormore different ambient-light sensor channels, in the same sensor array(which can be, e.g., a monolithic ASIC sensor array). Since the channelsof different types are in the same sensor array, the channels can beinherently aligned with each other to high precision. Different channelscan be tuned (e.g., using optical filters) to be sensitive to lighthaving specific properties, such as a particular range of wavelengths(which can be a wide or narrow band as desired), a particularpolarization property (e.g., linearly polarized in a certain direction,circularly polarized, etc.), or the like. The sensor array can be usedin combination with imaging optics to generate images that contain pixeldata corresponding to each channel type. Images produced from differentsensor types in the same sensor array are “inherently” registered toeach other by virtue of the channel alignment in the sensor array. Thatis, the spatial relationship between pixels (or channels) of differenttypes is established in the design of the sensor array and can be usedto map pixel data from different sensor types onto the same pixellocation within a field of view.

In some embodiments, some or all of the channel can have achannel-specific (or channel-type-specific) compensating micro-opticthat depends on the location of the channel in the array and/or theparticular wavelength range to which the channel is tuned. Suchmicro-optics can be used, e.g., to compensate for chromatic aberration,focal plane curvature, or other optical properties of the bulk imagingoptics.

In some embodiments, different ambient-light sensor channels can betuned to different overlapping wavelength bands (e.g., using opticalfilters with overlapping passbands), and arithmetic logic circuits canbe used to determine light intensity in various wavelength bands basedon the measurements in the overlapping wavelength bands.

In some embodiments, a ranging/imaging system can scan a field of viewusing a multispectral sensor array, e.g., by rotating the sensor arrayabout an axis transverse to the rows. During this motion, a givenlocation in space can be successively imaged by each of the channeltypes, thereby providing a multispectral image set with inherentregistration between imaging modalities (or channels). The spatialrelationship of the channels in the array, optical properties of theimaging optics (e.g., a focal length distortion profile of a bulkimaging optic), and the imaging rate relative to motion (e.g., rotation)of the sensor array can be selected so that the data from differentchannels maps easily onto a uniform grid of pixels representing thefield of view.

In some embodiments where the multispectral sensor array is scanned, agroup of two or more ambient-light sensor channels in a row can have thesame type of optical filter and apertures of subpixel size that arepositioned differently for different ambient-light sensor channels inthe group. Based on light-intensity measurements (e.g., photon counts)from the ambient-light sensor channels in the group, an ambient-lightimage with increased resolution in the scanning and/or non-scanningdirections can be obtained.

In some embodiments, a “2D” (two-dimensional) multispectral sensor arraycan be provided, where the array includes a two-dimensional arrangementof multispectral pixels. Each multispectral pixel can include a depthchannel along with one or more ambient-light sensor channels. Sucharrays can be used in moving (e.g., rotating) ranging/imaging systems aswell as in “static” systems, where imaging of the field of view isaccomplished without moving the sensor array.

Some embodiments relate to a sensor array with sensor channels arrangedin a number of sensor rows. Each sensor row can include a ranging sensorchannel (e.g., LIDAR sensor channel) and a set of one or moreambient-light sensor channels. Each ambient-light sensor channel caninclude an aperture (e.g., to define a field of view for the channel), aphotosensor (e.g., one or more single-photon avalanche diodes), achannel-specific optical filter that selectively passes light having achannel-specific property (e.g., a desired color, polarization state, orthe like). In some embodiments, some or all of the sensor channels caninclude a channel-specific micro-optic element to direct light havingthe channel-specific property through the aperture and toward thephotosensor, e.g., compensating for chromatic aberration in a bulkimaging optic that may be placed in front of the array. In someembodiments, the ambient-light sensor channels are multispectralchannels that include multiple photosensors tuned (e.g., using patternedoptical filters) to detect light having different properties. In someembodiments, the sensor array can include a 2D array of “hybrid” sensorchannels that include one group of photosensors configured for depthoperation (e.g., LIDAR sensing) and one or more other groups ofphotosensors configured for sensing of ambient light having variouscharacteristics. Sensor arrays of the kind described herein can beincorporated into light ranging/imaging systems and/or other opticalsystems.

Some embodiments relate to a light-sensor array having an arrangement ofsensor channels and a corresponding arrangement of apertures in anaperture plane. A bulk optic module can be used to direct and focuslight from a region being imaged onto the sensor array. If the bulkoptic module has a curved focal plane, channel-specific micro-opticelements of varying prescription and/or varying offset distance from theaperture plane can be placed in front of the apertures to correct for anoffset between the location of the aperture and a corresponding locationon the curved focal plane. Similarly, a light-emitter array can have anarrangement of emitter channels (e.g., narrow-band emitters that producelight at wavelengths usable for LIDAR applications) and a correspondingarrangement of apertures in an aperture plane. A bulk optic module canbe used to direct emitted light that passes through the apertures into aregion being imaged. If the bulk optic module has a curved focal plane,channel-specific micro-optic elements of varying prescription and/orvarying offset distance from the aperture plane can be placed in frontof the apertures to correct for an offset between the location of theaperture and a corresponding location on the curved focal plane. In suchembodiments, the prescription (e.g., focusing power) and/or a standoffdistance of the channel-specific micro-optic elements from the apertureplane can be varied, e.g., as a function of a radial distance from theoptical axis in the aperture plane. This can improve the efficiency oflight emission and/or light collection. Channel-specific micro-optics tocorrect for focal plane curvature of a bulk optic module can be employedin light receiving modules and/or light transmitting modules, regardlessof the particular characteristics of the light emitters or sensors. Insome embodiments where different channels are tuned to emit or receivelight of different wavelengths, the channel-specific micro-opticelements can correct for both focal plane curvature and chromaticaberration that may be present in a bulk optic module.

Some embodiments relate to a sensor array having sensor rows. Eachsensor row includes a LIDAR sensor channel and a set of one or moreambient-light sensor channels (e.g., one, three, five, six or more).Each ambient-light sensor channel includes a channel input aperture, aphotosensor, and a channel-specific optical filter that selectivelypasses light having a channel-specific property to the photosensor. Thephotosensor of each ambient-light sensor channel can be, for example,one or more photodiodes, such as one or more single-photon avalanchediodes (SPADs) operated in a photon-counting mode. In some embodiments,each LIDAR sensor channel can also include one or more SPADs operated ina photon-counting mode, and the same type of photosensors can be usedfor both LIDAR sensor channels and ambient-light sensor channels.

In some embodiments, the set of ambient-light sensor channels caninclude at least two ambient-light sensor channels, each having adifferent channel-specific optical filter. For example, the set ofambient-light sensor channels can include a red channel in which thechannel-specific optical filter selectively passes red light, a greenchannel in which the channel-specific optical filter selectively passesgreen light, and a blue channel in which the channel-specific opticalfilter selectively passes blue light. As another example, the set ofambient-light sensor channels includes at least five different colorchannels, wherein the channel-specific optical filter for each of the atleast five different color channels selectively passes light having adifferent range of wavelengths (referred to as a passband). Differentchannel-specific optical filters can have overlapping passbands ornon-overlapping passbands as desired, and a particular optical filtercan have a broad passband (e.g., the entire visible light spectrum) or anarrow passband (e.g., 25 nm or less, such as a passband correspondingto the emission spectrum of a typical light-emitting diode (LED)). Forinstance, a first color channel may have an optical a firstchannel-specific optical filter that selectively passes light having afirst range of wavelengths while a second color channel has a secondchannel-specific optical filter that selectively passes light having asecond range of wavelengths. The second range can correspond to anabsorption band of a particular substance, and data from the two colorchannels can be used in identifying substances.

In some embodiments, ambient-light sensor channels can also beselectively sensitive to properties of light other than wavelength. Forexample, the set of ambient-light sensor channels can include one ormore polarization channels in which the channel-specific optical filterselectively passes light having a particular polarization property.Color channels and polarization channels can be provided in combinationto provide information about both spectral and polarization propertiesof ambient light.

In some embodiments, the ambient-light sensor channels of a row caninclude a “multispectral” sensor channel, which can include multiplephotosensors and a patterned optical filter, with different portions ofthe patterned optical filter selectively passing light having differentproperties to different subsets of the photosensors in the multispectralsensor channel. The different portions of the patterned optical filtercan include, e.g., a first portion that passes light in a firstwavelength band and a second portion that passes light in a secondwavelength band (which may be partially overlapping wavelength bands), aportion that passes light having a particular polarization property, andso on.

Sensor channels in the array can be arranged as desired. For example, inembodiments where the set of one or more ambient-light sensor channelsincludes at least two ambient-light sensor channels, each having adifferent channel-specific optical filter, the ambient-light sensorchannels in a given sensor row can be spaced apart from each other by auniform pitch. The LIDAR sensor channel in a given sensor row can bespaced apart from a nearest one of the ambient-light sensor channels inthe given sensor row by the uniform pitch or by a distance that is aninteger multiple of the uniform pitch. Adjacent sensor rows can also bespaced apart from each other by the uniform pitch. This can allow foruniform sampling of object space when the sensor array is used in ascanning operation.

In some embodiments, the sensor array is fabricated as a single ASIC.The ASIC may also include other components, such as a data bufferdisposed within the ASIC and configured to store data from two or moreof the LIDAR sensor channels and two or more of the ambient-light sensorchannels and/or a processing circuit disposed within the ASIC andconfigured to perform an image processing operation on the data storedin the data buffer.

Some embodiments relate to a ranging/imaging system having a stationarybase, a sensor array rotationally coupled to the stationary base, a bulkoptical module, and a controller. The sensor array can be a sensor arraythat includes sensor rows, where each sensor row has a LIDAR sensorchannel and a set of one or more ambient-light sensor channels withchannel-specific optical filtering. The bulk optical module can bedisposed in front of the sensor array and configured to focus incidentlight on an aperture plane common to the LIDAR sensor channels and theambient-light sensor channels. The controller can synchronize rotationof the sensor array and operation of the photosensors such that a givenlocation in space relative to the stationary base is successively imagedby the LIDAR sensor channel and each of the ambient-light sensorchannels in one of the sensor rows. The controller can also beconfigured to generate multispectral image pixel data that includesper-pixel light intensity data determined using the ambient-light sensorchannels of the sensor array and per-pixel depth data determined usingthe LIDAR sensor channels of the sensor array. In some embodiments, theambient-light sensor channels in a given sensor row are spaced apartfrom each other by a uniform pitch, and the controller is furtherconfigured to rotate the ranging/imaging system such that successiveimaging operations occur at angular positions separated by a pitch anglecorresponding to the uniform pitch. The LIDAR sensor channel in a givensensor row can be spaced apart from a nearest one of the ambient-lightsensor channels in the given sensor row by the uniform pitch or by adistance that is an integer multiple of the uniform pitch. In someembodiments, adjacent sensor rows are also spaced apart from each otherby the uniform pitch.

Some embodiments relate to a sensor array having a two-dimensional arrayof hybrid sensor pixels. Each hybrid sensor pixel can include a LIDARsensor channel and a set of one or more ambient-light sensor channels,with each ambient-light sensor channel being tuned to selectivelymeasure intensity of light having a sensor-specific property. The sensorarray can also include readout electronics coupled to each hybrid sensorpixel in the two-dimensional array, and the readout electronics for eachhybrid sensor pixel can include: timing circuitry coupled to the LIDARsensor channel and configured to time arrival of photons at the LIDARsensor channel and to store data representing photon arrival times in amemory; and counter circuitry coupled to the ambient-light sensorchannel and configured to count a number of photons detected at theambient-light sensor channel and to store photon counts in the memory.

In some embodiments, the two-dimensional array of hybrid sensor pixelsis formed as a single ASIC. Each hybrid sensor pixel can include aplanar array of photosensors and a patterned optical filter, wheredifferent portions of the patterned optical filter selectively passlight having different properties to different subsets of thephotosensors in the planar array. The patterned optical filter can bearranged such that a first subset of the photosensors receives infraredlight within a narrow passband matched to a wavelength of a LIDARemitter, thereby providing the LIDAR sensor channel, and a second subsetof the photosensors receives visible light from at least a portion of avisible light spectrum, thereby providing one of the ambient-lightsensor channels. In some embodiments, the first subset of thephotosensors is located in a central region within a pixel area of thehybrid sensor pixel and the second subset of the photosensors arelocated in a peripheral region around the central region within thepixel area. In some embodiments, the second subset of the photosensorsincludes two or more photosensors, and the patterned optical filter isfurther arranged such that each of the two or more photosensors in thesecond subset receives light having a different property, such asdifferent ranges of wavelengths or different polarization properties.

In some embodiments, the LIDAR sensor channels for the two-dimensionalarray of hybrid sensor channels are formed as a first ASIC, and theambient-light sensor channels are formed as a second ASIC that isoverlaid on and aligned with the first ASIC. The second ASIC can have aplurality of apertures formed therein to allow light to pass into theLIDAR sensor channels.

Some embodiments relate to a ranging/imaging system that includes asensor array having a two-dimensional array of hybrid sensor pixels anda controller. Each hybrid sensor pixel can include a planar array ofphotosensors and a patterned optical filter, where different portions ofthe patterned optical filter selectively pass light having differentproperties to different subsets of the photosensors in the planar array.The patterned optical filter can be arranged such that a first subset ofthe photosensors receives infrared light within a narrow passbandmatched to a wavelength of a LIDAR emitter, thereby providing the LIDARsensor channel, and a second subset of the photosensors receives visiblelight from at least a portion of a visible light spectrum, therebyproviding one of the ambient-light sensor channels. The controller canbe configured to operate the LIDAR sensor channels and the ambient-lightsensor channels such that a given location within a field of view isimaged by the LIDAR sensor channel and the ambient-light sensor channelsof one of the hybrid sensor pixels. In some embodiments, theranging/imaging system also includes an emitter to emit light detectableby the LIDAR sensor channels, and the controller can be furtherconfigured to coordinate operation of the emitter with operation of theLIDAR sensor channels to determine a depth measurement for each hybridsensor pixel. The controller can also be configured to operate theemitter and the LIDAR sensor channels to perform electronic scanning ofa field of view such that different portions of the field of view areimaged by different ones of the LIDAR sensor channels at differenttimes.

Some embodiments relate to an imaging system that has a stationary base,a sensor array rotationally coupled to the stationary base, a bulkoptical module, and a controller. The sensor array can have a pluralityof sensor rows, each sensor row including a set of one or moreambient-light sensor channels, each of which can include a channel inputaperture, a photosensor, and a channel-specific optical filter thatselectively passes light having a channel-specific property to thephotosensor. The bulk optical module can be disposed in front of thesensor array and configured to focus incident light on an aperture planecommon to the ambient-light sensor channels. The controller can beconfigured to synchronize rotation of the sensor array and operation ofthe photosensors to generate image pixel data that includes lightintensity data determined using the ambient-light sensor channels. Insome embodiments, the set of one or more ambient-light sensor channelsincludes at least two ambient-light sensor channels, with differentambient-light sensor channels having different channel-specific opticalfilters. The ambient-light sensor channels in a given sensor row arespaced apart from each other by a uniform pitch. In some embodiments,adjacent sensor rows are also spaced apart from each other by the sameuniform pitch. This can facilitate uniform sampling of a field of view.In some embodiments, the imaging system can also include: a data bufferdisposed within the ASIC and configured to store data from two or moreof the ambient-light sensor channels; and a processing circuit disposedwithin the ASIC and configured to perform an image processing operationon the data stored in the data buffer.

Some embodiments relate to an imaging system that includes a sensorarray, a bulk optic module, a controller, and multiple channel-specificmicro-optic elements. The sensor array can have sensor channels arrangedto receive light through corresponding apertures in an aperture plane.The bulk optic module can be disposed in front of the sensor array andconfigured to focus incident light on the aperture plane to form animage of a field of view. The controller can operate the sensor array togenerate image data for the field of view. Each of the channel-specificmicro-optic element can be disposed in front of a different one of theapertures and can have an optical prescription that is different fordifferent sensor channels. The optical prescription for a particular oneof the channel-specific micro-optic elements can be based at least inpart on an optical property of the bulk optic module, such as chromaticaberration (for sensor channels that are color-selective) and/or focalplane curvature (in which case the optical prescription can be afunction of radial distance from the optical axis of the bulk opticmodule). Optical prescriptions can include focal length (or focusingpower) and/or standoff distance.

In some embodiments, the sensor channels are arranged in sensor rows,with each sensor row including a LIDAR sensor channel and a set of oneor more ambient-light sensor channels, where each ambient-light sensorchannel includes a channel input aperture, a photosensor, and achannel-specific optical filter that selectively passes light having achannel-specific property to the photosensor. Channel-specificmicro-optic elements can be provided for at least some of theambient-light sensor channels. For instance, the channel-specificmicro-optic element for each ambient-light sensor channel can have aprescription that is based at least in part on the channel-specificoptical filter, e.g., to compensate for chromatic aberration of the bulkoptic module.

In some embodiments, the sensor channels include LIDAR sensor channels,and at least some of the LIDAR sensor channels can have correspondingchannel-specific micro-optic elements with respective opticalprescriptions based in part on a LIDAR operating wavelength and in parton an optical characteristic of the bulk optical module.

Some embodiments relate to a LIDAR transmitter device that includes anemitter array, a bulk optic module, and channel-specific micro-opticelements. The emitter array can have a plurality of emitter channelsarranged to emit light through a corresponding plurality of apertures inan aperture plane. The bulk optic module can be disposed in front of theemitter array and configured to direct light from the aperture planeinto a field of view. The channel-specific micro-optic elements can eachbe disposed in front of a different one of the apertures and each canhave an optical prescription that is different for different emitterchannels. The optical prescriptions of the channel-specific micro-opticelements can be based at least in part on an optical property of thebulk optic module. For instance, if the bulk optic module has a curvedfocal plane, the optical prescription of each of the channel-specificmicro-optic elements can compensate for an offset between a location ofthe aperture and a corresponding location on the curved focal plane,e.g., by using an optical prescription for each channel-specificmicro-optic element that is a function of a radial distance in theaperture plane from an optical axis of the bulk optic module to thecorresponding aperture. Optical prescriptions can include focal length(or focusing power) and/or standoff distance; accordingly, thechannel-specific micro-optic elements disposed in front of differentapertures can have optical prescriptions with different focusing powerand/or different standoff distances from the aperture plane.

Some embodiments relate to a scanning imaging system for providing animage having a fixed resolution in a scanning direction. The scanningimaging system can include a sensor array, a rotary control system, anda bulk optic module. The sensor array can include a set of sensorchannels arranged in two dimensions, where each sensor channel isconfigured to detect light (with the same characteristics or differentcharacteristics). The rotary control system can be configured to rotatethe sensor array in a scanning direction through a sequence of angularmeasurement positions to obtain a frame of data that represents an imageof a field of view, such as a grid of image pixels that are spaced inthe scanning direction according to a uniform angular pitch. The bulkoptic module can be configured to focus the light toward the sensorarray and can have a focal length and a focal length distortion profilethat are both tuned to the arrangement of the set of sensor channelssuch that rotating the sensor array through the uniform angular pitchalong the scanning direction shifts a location where a ray is incidenton the sensor array from one sensor channel to an adjacent sensorchannel.

The set of sensor channels can include various combinations of channeltypes. For instance, the set of sensor channels can includes a staggeredgrid of LIDAR sensor channels defining a column that extends in adirection transverse to the scanning direction. In addition (orinstead), the set of sensor channels can include one or moreambient-light sensor channel disposed along the scanning directionrelative to each of the LIDAR sensor channels.

In some embodiments, the sensor array has a fixed pitch between adjacentsensor channels along the scanning direction, and the bulk optic modulehas either an F θ focal length distortion profile or an F tan θ focallength distortion profile.

In other embodiments, the sensor array may have a variable distancebetween adjacent sensor channels. For example, if the focal lengthdistortion profile of the bulk optic module exhibits barrel distortion,a distance between adjacent sensor channels in the sensor array canincrease from an edge to a center of the sensor array. Similarly, if thefocal length distortion profile of the bulk optic module exhibitspincushion distortion, a distance between adjacent sensor channels inthe sensor array can decrease from an edge to a center of the sensorarray. Such arrangements can provide uniform sampling of the objectspace.

Some embodiments relate to a scanning imaging system for providing animage having a fixed resolution in a scanning direction. The scanningimaging system can include a sensor array, a mirror subsystem, and abulk optic module. The sensor array can include a set of sensor channelsarranged in one or two dimensions, each sensor channel being configuredto detect light (with the same characteristics or differentcharacteristics). The mirror subsystem can be configured to direct lightfrom different portions of a field of view onto the sensor array atdifferent times such that the sensor array obtains a frame of datarepresenting an image of the field of view, where the frame of data canbe, e.g., a grid of image pixels spaced in a scanning directionaccording to a uniform angular pitch. The bulk optic module can beconfigured to focus the light toward the sensor array and can have afocal length and a focal length distortion profile that are both tunedto the arrangement of the set of sensor channels such that rotating thesensor array through the uniform angular pitch along the scanningdirection shifts a location where a ray is incident on the sensor arrayfrom one sensor channel to an adjacent sensor channel.

The set of sensor channels can include various combinations of channeltypes. For instance, the set of sensor channels can includes a staggeredgrid of LIDAR sensor channels defining a column that extends in adirection transverse to the scanning direction. In addition (orinstead), the set of sensor channels can include one or moreambient-light sensor channel disposed along the scanning directionrelative to each of the LIDAR sensor channels.

In some embodiments, the sensor array has a fixed pitch between adjacentsensor channels along the scanning direction, and the bulk optic modulehas either an F θ focal length distortion profile or an F tan θ focallength distortion profile.

In other embodiments, the sensor array may have a variable distancebetween adjacent sensor channels. For example, if the focal lengthdistortion profile of the bulk optic module exhibits barrel distortion,a distance between adjacent sensor channels in the sensor array canincrease from an edge to a center of the sensor array. Similarly, if thefocal length distortion profile of the bulk optic module exhibitspincushion distortion, a distance between adjacent sensor channels inthe sensor array can decrease from an edge to a center of the sensorarray. Such arrangements can provide uniform sampling of the objectspace.

Some embodiments relate to a raster-scanning imaging system forproviding an image having a fixed resolution by scanning in twodimensions. The raster-scanning imaging system can include a sensorarray, a raster scanning mechanism, and a bulk optic module. The sensorarray can include a set of sensor channels arranged in one or twodimensions, with each of the sensor channels being configured to detectlight. The raster scanning mechanism can be configured to perform araster scan in one or two dimensions that directs light from differentportions of a field of view onto the sensor array at different timessuch that the sensor array obtains a frame of data representing an imageof the field of view, where the frame of data can be, e.g., atwo-dimensional grid of image pixels spaced in each of the twodimensions according to a uniform pitch, with both dimensions of thegrid of image pixels being larger than the dimensions of the sensorarray. The bulk optic module can be configured to focus the light towardthe sensor array and can have a focal length and a focal lengthdistortion profile that are both tuned to the arrangement of the set ofsensor channels such that the sensor array uniformly samples the fieldof view.

In some embodiments, the raster scanning can operate by moving thesensor array in two dimensions to point the sensor channels at differentportions of the field of view. In other embodiments, the raster scanningmechanism can include a tip-tilt mirror movable in two dimensions todirect light from different portions of a field of view onto the sensorarray at different times.

The set of sensor channels can include various combinations of channeltypes. In some embodiments, the sensor channels include LIDAR sensorchannels and may also include ambient-light sensor channels of varioustypes. In other embodiments, the sensor channels can include one or more“hybrid” sensor channels, where each hybrid sensor channel has multiplephotosensors and a patterned optical filter wherein different portionsof the patterned optical filter selectively pass light having differentproperties, the patterned optical filter being arranged such thatdifferent photosensors receive light having different properties. Thepatterned optical filter can be further arranged such that a firstsubset of the plurality of photosensors receives infrared light within anarrow passband matched to a wavelength of a LIDAR emitter and a secondsubset of the plurality of photosensors receives visible light from atleast a portion of a visible light spectrum. As another example, hybridsensor channels can include: a LIDAR sensor channel disposed on a firstsensor channel layer; an aperture layer overlying the first sensorchannel layer and having an aperture therein to allow light to enter theLIDAR sensor channel; and ambient-light sensor channels disposed on atleast a portion of the aperture layer around the aperture, eachambient-light sensor channel including a photosensor and an opticalfilter that selectively passes light having a specific property, wherethe optical filters of different ones of the ambient-light sensorchannels selectively pass light having different properties.

In some embodiments, the sensor array of the raster-scanning imagingsystem has a fixed pitch between sensor channels, and the bulk opticmodule has either an F tan θ focal length distortion profile or an F θfocal length distortion profile.

Some embodiments relate to a sensor array having multiple sensor rows, alogic circuit, and a controller. Each sensor-row can include a group oftwo or more enhanced-resolution ambient-light sensor channels sensitiveto a range of wavelengths, and each enhanced-resolution ambient-lightsensor channel in the group can include: a channel-specific inputaperture, wherein the channel-specific input apertures of differentenhanced-resolution ambient-light sensor channels in the group exposedifferent portions of a channel area; and a photosensor. The logiccircuit can determine multiple subpixel light intensity values based onintensity data from the photosensors in the group of enhanced-resolutionambient-light sensor channels. The controller can be configured toperform a scanning operation that exposes the sensor array to differentareas within a field of view at different times such that eachambient-light sensor channel in the group of two or moreenhanced-resolution ambient-light sensor channels in a particular row isexposed to a same pixel area within the field of view at differenttimes.

In some embodiments, each enhanced-resolution ambient-light sensorchannel in the group can include an optical filter that selectivelypasses light having a specific property, with the specific propertybeing the same for every enhanced-resolution ambient-light sensorchannel in the group.

In some embodiments, the different portions of the channel area exposedby the apertures of different enhanced-resolution ambient-light sensorchannels in the group are non-overlapping portions of the channel area.For instance, the group of enhanced-resolution ambient-light sensorchannels can include four enhanced-resolution ambient-light sensorchannels and the non-overlapping portions can correspond to differentquadrants of the channel area.

In other embodiments, the different portions of the channel area exposedby the apertures of different enhanced-resolution ambient-light sensorchannels in the group can include overlapping portions of the channelarea. An arithmetic logic circuit can be provided to decode intensityvalues for a set of non-overlapping portions of the channel area basedon sensor data from the group of two or more enhanced-resolutionambient-light sensor channels. To facilitate decoding, one (or more) ofthe enhanced-resolution ambient-light sensor channels in the group canhave an aperture that exposes the entire channel area.

In some embodiments, each sensor row further comprises a LIDAR sensorchannel spatially registered with the group of enhanced-resolutionambient-light sensor channels. The LIDAR sensor channels can provide adepth image having a first resolution while the enhanced-resolutionambient-light sensor channels provide an intensity image having a secondresolution higher than the first resolution in the row-wise directionand/or in a direction transverse to the sensor rows.

Some embodiments relate to a scanning imaging system that includes asensor array, an arithmetic logic circuit, and a controller. The sensorarray can include a group of two or more enhanced-resolutionambient-light sensor channels sensitive to a range of wavelengths, eachof which can include: a channel-specific input aperture, where thechannel-specific input apertures of different enhanced-resolutionambient-light sensor channels in the group expose different portions ofa channel area; a photosensor; and two or more registers to accumulatephoton counts from the photosensor during a time interval that issubdivided into two or more time bins, where each of the registersaccumulates photon counts during a different one of the time bins. Thearithmetic logic circuit can compute a plurality of subpixel lightintensity values based on the photon counts accumulated in the pluralityof registers of all of the enhanced-resolution ambient-light sensorchannels in the group. The controller can be configured to perform ascanning operation that exposes the sensor array to different areaswithin a field of view at different times such that each ambient-lightsensor channel in the group of two or more enhanced-resolutionambient-light sensor channels is exposed to a same pixel area within thefield of view at different times.

In some embodiments, each enhanced-resolution ambient-light sensorchannel in the group can include an optical filter that selectivelypasses light having a specific property, with the specific propertybeing the same for every enhanced-resolution ambient-light sensorchannel in the group.

In some embodiments, the scanning imaging system can also include aLIDAR sensor channel spatially registered with the group ofenhanced-resolution ambient-light sensor channels. The LIDAR sensorchannels can provide a depth image having a first resolution while theenhanced-resolution ambient-light sensor channels provide an intensityimage having a second resolution higher than the first resolution in oneor two dimensions.

The different portions of the channel area exposed by the apertures ofdifferent enhanced-resolution ambient-light sensor channels in the groupcan include overlapping and/or non-overlapping portions of the channelarea. For example, the group of two or more enhanced-resolutionambient-light sensor channels can include four ambient-light sensorchannels, the two or more registers can include four registers, and thearithmetic logic circuit can compute sixteen subpixel light intensityvalues. If, for instance, the channel-specific input aperture of a firstone of the enhanced-resolution ambient-light sensor channels exposes aquarter of the channel area and wherein the respective channel-specificinput apertures of a second, a third, and a fourth one of theenhanced-resolution ambient-light sensor channels each exposes adifferent portion of the quarter of the channel area, the sixteensubpixel light intensity values can provide a four-by-four gridcorresponding to the channel area.

Some embodiments relate to a sensor array having multiple sensor rows.Each sensor row can include a set of at least two ambient-light sensorchannels, and each ambient-light sensor channel in the set can include achannel input aperture, a photosensor, and a channel-specific opticalfilter that selectively passes light having a channel-specific propertyto the photosensor. The set of at least two ambient-light sensorchannels in each sensor row can include at least two overlappingambient-light sensor channels having respective channel-specific opticalfilters for which the channel-specific property of the light overlaps.The sensor array can also include an arithmetic logic circuit that candecode signals from the three or more ambient-light sensor channels intorespective light intensity levels for light having a plurality ofnon-overlapping properties.

In some embodiments, channel-specific property includes a wavelengthrange of light. The set of at least two overlapping ambient-light sensorchannels includes a first color channel having a first channel-specificoptical filter that selectively passes light having a first range ofwavelengths, a second color channel having a second channel-specificoptical filter that selectively passes light having a second range ofwavelengths, and a third color channel having a third channel-specificoptical filter that selectively passes light having a third range ofwavelengths, where the first range of wavelengths and the second rangeof wavelengths are partially overlapping, and wherein the third range ofwavelengths encompasses both of the first range of wavelengths and thesecond range of wavelengths. For example, the third wavelength band cancorrespond to the visible light spectrum.

In some embodiments, the channel-specific property can be a differentproperty such as a polarization property of light.

In some embodiments, each sensor row further comprises a LIDAR sensorchannel, and depth data determined from the LIDAR sensor channels can beinherently registered with intensity data determined from theambient-light sensor channels.

Some embodiments relate to an imaging system that includes a sensorarray, a controller, and an arithmetic logic circuit. The sensor arraycan have a plurality of sensor rows. Each sensor row can include a setof at least two ambient-light sensor channels, with each ambient-lightsensor channel including: a channel input aperture; a photosensor; and achannel-specific optical filter that selectively passes light having achannel-specific property to the photosensor. The set of at least twoambient-light sensor channels in each sensor row can include at leasttwo overlapping ambient-light sensor channels having respectivechannel-specific optical filters for which the channel-specific propertyof the light overlaps. The controller can operate the sensor array suchthat each of the three or more ambient-light sensor channels is exposedto light from a same portion of a field of view. The arithmetic logiccircuit can decode signals from the at least two overlappingambient-light sensor channels into respective light intensity levels forlight having a plurality of non-overlapping properties.

Some embodiments relate to a sensor array that includes multiple sensorchannels including multispectral sensor channels. Each multispectralsensor channel can have: a channel input aperture; at least threephotosensors; and a patterned optical filter having at least threedifferent portions, wherein different portions of the patterned opticalfilter selectively pass light having different properties to differentsubsets of the at least three photosensors. The different portions ofthe patterned optical filter can include at least a first portion thatpasses light to a first subset of the at least three photosensors and asecond portion that passes light to a second subset of the at leastthree photosensors, where respective properties of light passed by thefirst and second portions overlap. An arithmetic logic circuit candecode signals from the first and second subsets of the photosensorsinto respective light intensity levels for light having a plurality ofnon-overlapping properties. As in other embodiments, the properties caninclude a wavelength range and/or a polarization property.

In some embodiments, the sensor channels can include plurality of LIDARsensor channels disposed such that each LIDAR sensor channel forms asensor row with a different one of the multispectral sensor channels,and depth data determined from the LIDAR sensor channels can beinherently registered with intensity data determined from theambient-light sensor channels.

In some embodiments, each multispectral sensor channel can include aLIDAR photosensor and the patterned optical filter can include a fourthportion that selectively passes light having a wavelength correspondingto a LIDAR emitter to the LIDAR photosensor.

The following detailed description will provide a better understandingof the nature and advantages of the claimed invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show simplified cross-section views of a singlemicro-optic sensor channel that can be included in a sensor arrayaccording to one or more of the embodiments described herein.

FIG. 2 shows a simplified front view of a sensor array according to oneor more of the embodiments described herein.

FIG. 3 shows a simplified side cross-section view of a sensor row of thesensor array of FIG. 2.

FIG. 4 shows a simplified top view of another sensor array according toone or more embodiments.

FIG. 5 shows a simplified top view of another sensor array according toone or more embodiments.

FIG. 6 shows a simplified top view of another sensor array according toone or more embodiments.

FIG. 7 shows a simplified top view of a multispectral sensor channelthat can be included in the sensor array of FIG. 6.

FIG. 8 shows a schematic side view of a portion of the sensor array ofFIG. 6.

FIG. 9 shows a simplified side cross section view of a portion of asensor array according to an embodiment of the present invention.

FIG. 10 shows a simplified top view of the sensor array of FIG. 9.

FIG. 11 shows an example of non-overlapping passbands for three filtersthat can be used to provide ambient-light intensity measurements in someembodiments,

FIG. 12 shows an example of overlapping passbands for three filters thatcan be used to provide ambient-light intensity measurements with encodedspectral information in some embodiments.

FIG. 13 shows a simplified front view of a sensor array according tosome embodiments.

FIGS. 14A and 14B show examples of a multispectral sensor channel havinga patterned optical filter according to some embodiments.

FIG. 15 shows a simplified side view of a light ranging/imaging devicethat can incorporate the sensor array of FIG. 2.

FIG. 16 is a simplified cross-sectional view of a portion of a sensorarray with channel-specific compensating micro-optics according to oneor more embodiments.

FIG. 17 is a simplified cross-sectional view of a portion of a sensorarray with channel-specific compensating micro-optics according to oneor more embodiments.

FIG. 18 is a simplified cross-sectional view of a portion of a sensorarray with channel-specific compensating micro-optics according to oneor more embodiments.

FIG. 19 is a simplified cross-sectional view of a portion of a sensorarray with an achromatic bulk optical module according to one or moreembodiments.

FIG. 20 is a simplified cross-sectional view of a portion of anothersensor array with an achromatic bulk optical module according to one ormore embodiments.

FIG. 21 shows an example of a sensor module with per-channelmicro-optics to correct for focal length of a bulk optic moduleaccording to one or more embodiments.

FIG. 22 shows another example of a receive module with channel-specificmicro-optic elements according to one or more embodiments.

FIG. 23 shows an example of a transmit module with channel-specificmicro-optic elements according to one or more embodiments.

FIGS. 24A and 24B are simplified conceptual illustrations showing thepotential for pointing error in a scanning system using a sensor array.

FIG. 25 is a simplified optical diagram showing a focal lengthdistortion property for a bulk optical module according to one or moreembodiments.

FIG. 26 shows an example of intrapixel pointing error that can bequantified and constrained in some embodiments of scanning systems.

FIGS. 27 and 28 show examples of sensor channel positioning tocompensate for barrel distortion and pincushion distortion in a bulkoptical module according to one or more embodiments.

FIG. 29 shows an example of raster scanning using a sensor arrayaccording to an embodiment of the present invention.

FIG. 30 shows a nonuniform sampling pattern that can result fromresulting from raster-scanning using an array with a bulk optic thatexhibits pincushion distortion.

FIGS. 31A and 31B show an example of a rotating imaging/LIDAR systemaccording to one or more embodiments; FIG. 31A is a simplified top viewand FIG. 31B is a simplified side view.

FIG. 32 illustrates a block diagram of a rotating imaging/LIDAR systemaccording to one or more embodiments.

FIGS. 33A and 33B illustrate an example of a hyperspectral imagingoperation using a sensor array according to one or more embodiments.

FIG. 34 shows a simplified front view of a sensor array according tosome embodiments.

FIG. 35 shows a set of four ambient-light sensor channels withspatially-encoded subpixel apertures according to some embodiments.

FIG. 36 shows a simplified schematic diagram of a readout data path withmultiple integration registers according to some embodiments.

FIG. 37 illustrates ambient light measurement using multiple integrationregisters according to some embodiments.

FIG. 38A shows a set of ambient-light sensor channels that providespatially-encoded subpixel apertures according to some embodiments.

FIG. 38B shows the effect of temporal subdivision using an ambient-lightsensor channel of FIG. 38A.

FIG. 39 shows an example of a static imaging/LIDAR system according toone or more embodiments.

FIG. 40 shows an example automotive application of static imaging/LIDARsystems according to one or more embodiments.

FIG. 41 shows another example automotive application of staticimaging/LIDAR systems according to one or more embodiments.

FIG. 42 shows an example of a static imaging/LIDAR system with expandedfield of view according to one or more embodiments.

FIG. 43 illustrates a block diagram of a static imaging/LIDAR systemaccording to one or more embodiments.

FIG. 44 shows an example of hyperspectral images that can be acquiredusing a multispectral ranging/imaging sensor array according to one ormore embodiments.

FIG. 45 shows an example of an image that has been annotated to identifymaterials contained therein.

DETAILED DESCRIPTION 1. Multispectral Sensor Arrays

As used herein, a multispectral sensor array refers to an array ofsensors, each of which is configured to image a portion (pixel) of afield of view at a different wavelength. Data from different sensorsthat image the same pixel can be combined to provide a multispectralpixel for an image. Examples of multispectral sensor arrays will now bedescribed. These examples illustrate and embody various principles andconcepts related to the construction of multispectral sensor arrays. Itwill become apparent that many other implementations of a multispectralsensor array are possible, and the examples provided are not intended tobe limiting.

1.1. Sensor Channel Examples

Examples of multispectral sensor arrays described herein include arraysconstructed from sensor channels formed or arranged on a monolithicsemiconductor device, such as an application-specific integrated circuit(ASIC). FIG. 1A shows a cross-section of a single micro-optic sensorchannel 100 that can be used in some embodiments of a multispectralsensor array. Sensor channel 100 accepts an input cone of lightpotentially containing a wide range of wavelengths, filters out all buta selected subset of the wavelengths (with the selected subset dependingon the particular channel), and allows a photosensor 152 (sometimesreferred to as a “pixel”) to detect only or substantially only photonswithin the selected subset of wavelengths. Embodiments of the inventionare not limited to any particular configuration for sensor channels, andsensor channel 100 is just one example of a sensor channel that can beimplemented in sensor array 200.

In some embodiments, sensor channel 100 includes an input aperture layer110 including an optically-transparent aperture 112 andoptically-non-transparent stop region 114. As used herein, the term“optically transparent” refers to a material that allows most or allincident light to pass through. As used herein, the term “opticallynon-transparent” refers to a material that allows little to no light topass through, e.g., a reflecting or absorbing surface. Aperture 112 isshaped and sized to define a narrow field of view when placed at thefocal plane of an imaging optic, examples of which are described below.Aperture layer 110 is configured to receive an input light cone asindicated by input marginal ray lines 120. In a multispectral sensorarray, examples of which are described below, aperture layer 110 mayinclude an array of optically-transparent apertures andoptically-non-transparent stop regions built upon a single monolithicpiece such as an optically-transparent substrate. In some embodiments,aperture layer 110 can be formed from a optically non-transparentmaterial that forms stop regions 114 and apertures 112 can be holes oropenings in layer 110.

In some embodiments, sensor channel 100 includes an optical lens layer130 including a collimating lens 132 characterized by a focal length.Collimating lens 132 can be offset from the plane of aperture 112 andstop region 114 by its focal length and aligned axially with aperture112 (i.e., the optical axis of the collimating lens is aligned with thecenter of the aperture). In this manner collimating lens 132 can beconfigured to collimate light rays passed by aperture 112 such that thelight rays are travelling approximately parallel to the optical axis ofcollimating lens 132. Optical lens layer 130 may optionally includeapertures, optically-non-transparent regions and tube structures toreduce cross talk between nearby sensor channels 100 in a sensor array.

In some embodiments, sensor channel 100 includes an optical filter layer140 including an optical filter 142. In some embodiments, optical filterlayer 140 is disposed on a detector side of optical lens layer 130(opposite the aperture side). Optical filter layer 140 can be configuredto pass normally incident photons at a specific operating wavelength andpassband. Optical filter layer 140 may contain any number of opticalfilters 142. The optical filter(s) in a particular instance of sensorchannel 100 can be selected based on the intended use of that particularinstance of sensor channel 100, e.g., as described below. Optical filterlayer 140 may optionally include apertures, optically-non-transparentregions and tube structures to reduce cross talk.

In some embodiments, sensor channel 100 includes a photosensor layer 150including one or more individual photosensors 152 disposed behindoptical filter layer 140. Each photosensor 152 can be a photosensorcapable of detecting photons with a detector active area made of, e.g.,one or more standard photodiodes, avalanche photodiodes (APDs),single-photon avalanche diodes (SPADs), RCPs (Resonant CavityPhotodiodes), optical nanoantennas, microbolometers, or other suitablephotodetectors. Photosensor 152 may be composed of several photondetector areas (e.g., each a different SPAD) cooperating together to actas a single sensor, often with higher dynamic range, faster responsetime, or other beneficial properties as compared to a single largephoton detection area. In addition to photosensors 152 for any number ofsensor channels, photosensor layer 150 can include optional structuresto improve detection efficiency and reduce cross talk with neighboringsensor channels. Photosensor layer 150 may optionally include diffusers,converging lenses, apertures, optically-non-transparent tube spacerstructures, optically-non-transparent conical spacer structures, etc.

Stray light may be caused by roughness of optical surfaces,imperfections in transparent media, back reflections, and so on, and maybe generated at many features within sensor channel 100 or external tosensor channel 100. The stray light can be directed through opticalfilter layer 140 along a path non-parallel to the optical axis ofcollimating lens 132; reflecting between aperture layer 110 andcollimating lens 132; and generally taking any other path or trajectorypossibly containing many reflections and refractions. If multiplereceiver channels are arrayed adjacent to one another, stray light inone receiver channel may be absorbed by a photosensor in anotherchannel, thereby contaminating the timing, phase, intensity, or otherinformation pertaining to received photons. Accordingly, sensor channel100 may also feature structures to reduce cross talk and increase signalbetween receiver channels. Examples of such structures and othersuitable receiver channels are described in U.S. patent application Ser.No. 15/979,295 entitled “Micro-optics for Imaging Module with MultipleConverging Lenses per Channel,” filed on May 14, 2018, the disclosure ofwhich is hereby incorporated by reference in its entirety for allpurposes.

The components and arrangement of sensor channel 100 can be modified asdesired. By way of illustration, FIG. 1B shows a cross-section of asingle micro-optic sensor channel 100′ that can be used in someembodiments of a multispectral sensor array. Micro-optic sensor channel100′ is generally similar to micro-optic sensor channel 100 of FIG. 1A,and parts have been given corresponding numbers. In this example, lenselement 132′ has a different configuration from lens 132 shown in FIG.1A, with a planar surface oriented toward the aperture and a convexsurface oriented toward optical filter layer 140. Similarly to lenselement 132, lens element 132′ collimates incident light and directs thecollimated light into optical filter layer 140, as indicated by marginalrays 120. It is to be understood that other modifications are alsopossible. For instance, optical lens layer 130 may include light guidesin addition to or instead of lens elements, optical filters may beplaced on the aperture side of optical lens layer 130, and so on. Asanother example, a sensor channel need include any micro-optic elementsand may be as simple as a photosensor (or group of photosensors) with anoptical filter disposed thereon. In some instances, optical filters maybe fabricated within the metal layers of the photosensor (e.g., in thecase of polarization channels described below). Additional examples ofalternative sensor channel configurations are shown below. It is also tobe understood that different sensor channels in the same sensor arraycan have different configurations.

1.2. Example Multispectral Sensor Arrays

In some embodiments, a multispectral sensor array incorporates a groupof aligned sensor channels fabricated on a common substrate. Sensorchannels tuned to different wavelengths or wavelength ranges (alsoreferred to herein as “sensor types”) can be arranged at differentlocations on the substrate, with the locations selected such that agiven portion of the field of view can be viewed by different sensorchannels either at the same time or at different times. Many specificarrangements are possible; examples will now be described.

1.2.1. Row-based Multispectral Sensor Arrays

FIG. 2 shows a simplified front view of a sensor array 200 according toan embodiment of the present invention. Sensor array 200 can include anumber of LIDAR sensor channels 202; this example shows sixteen LIDARsensor channels 202, but any number of LIDAR sensor channels 202 can beincluded. In this example, LIDAR sensor channels 202 are arranged in astaggered fashion; however, this is not required, and in someembodiments, LIDAR sensor channels 202 can be arranged in a singlecolumn (in this example, columns run parallel to the z axis shown at theleft side of FIG. 2).

In this example, each LIDAR sensor 202 is associated with a “row” 204 ofsensor array 200. (The term “row” here is used to indicate a linear orapproximately linear arrangement of elements; rows in FIG. 2 areindicated by dashed lines.) In addition to a LIDAR sensor 202, each rowof sensor array 200 includes one or more ambient-light sensor channels206. In this example, ambient-light sensor channels 206R detect redlight, ambient-light sensor channels 206G detect green light, andambient-light sensor channels 206B detect blue light; however, anynumber and combination of ambient-light sensor channels can be used.Additional examples are described below. Each row can include a completeset of sensors for generating a multispectral pixel, and sensor arrayssuch as sensor array 200 are referred to herein as “row-based” or “1D”sensor arrays.

FIG. 3 shows a simplified side cross-section view of a row 204 of sensorarray 200 of FIG. 2. Each sensor channel 206R/G/B, 202 of sensor array200 can be implemented as a separate instance of sensor channel 100described above. In some embodiments, different sensor channels206R/G/B, 202 differ in having different optical filters. For instance,optical filter 342L for a LIDAR sensor channel 202 can include, e.g., aBragg reflector type filter or the like to pass light at the LIDARsignaling wavelength with a narrow passband. The optical filter for agiven ambient-light sensor channel can include a bandpass filter thatpasses light within a given region of the spectrum and blocks lightoutside the bandpass region. For instance, for red-light sensor channel206R, optical filter 342R can pass light having wavelengths in the redregion of the spectrum (e.g., wavelengths from about 620 nm to about 750nm); for green-light sensor channel 206G, optical filter 342G can passlight having wavelengths in the green region (e.g., wavelengths fromabout 495 nm to about 570 nm); and for blue-light sensor channel 206B,optical filter 342B can pass light having wavelengths in the blue region(e.g., wavelengths from about 450 nm to about 495 nm). Those skilled inthe art will appreciate that the particular bandpass filter for a givencolor can be selected as desired, and different embodiments can includesensor channels “tuned” (by application of appropriate optical filters)to any desired range of light wavelengths, including non-visible lightwavelengths such as ultraviolet, near infrared (NIR), shortwave infrared(SWIR), midwave infrared (MWIR), or longwave infrared (LWIR, i.e.,thermal imaging), and the different wavelength ranges associated withdifferent types of sensor channels in a given sensor array may or maynot overlap. Optical systems of the kind described herein can operate inwavelength ranges extending from 300 nm to 20 μm, provided that theoptical elements are selected to function at the operational wavelengthsand the photosensors are capable of sensing electromagnetic energy atthose same wavelengths. Materials and sensors suitable for allwavelengths in this range are known in the art, and the same opticalprinciples (ray optics, refraction, etc.) apply. Other ambient-lightsensor channels can be tuned to detect other properties of light;examples are described below.

Input aperture layer 310 can correspond to input aperture layer 110 ofFIG. 1A (or FIG. 1B), and a single input aperture layer 310 can providean aperture 312R/G/B, 312L for each sensor channel 206R/G/B, 202 ofsensor array 200 such that these apertures are in the same plane. Insome embodiments, aperture layer 310 can have a thickness d, andapertures 312R/G/B/L can be formed with tapered openings such that, atexit surface 360 of aperture layer 310, the exit aperture width can bewider than the aperture, e.g., as wide as the respective sensor channels(as shown at 362R/G/B/L). Alternatively, the direction of taper can bereversed so that the aperture is widest at the input side and narrowstoward the sensor channel. The aperture can follow the ray cone definedby the marginal rays of each channel, thereby defining a numericaperture for the channel that is matched to the numeric aperture of thechannel optics 332 and a bulk optical element that directs light ontothe sensor array (examples of which are described below). The particularthickness and structure of aperture layer 310 can be varied as desired.

In some embodiments, channel-specific compensating micro-optic elements370R, 370G, and 370B can be placed directly in front of input apertures312R/G/B. As described below, such channel-specific micro-optic elementscan provide improved light collection efficiency, e.g., by compensatingfor chromatic aberration in a bulk optic of the system.

In some embodiments, sensor array 200 can be fabricated as part of amonolithic device on a single substrate using, for example, CMOStechnology. The monolithic device can include an array of photosensors152 together with a processor and a memory (not shown in FIGS. 2-3) forprocessing the raw signals from individual photosensors 152 (or groupsof photosensors 152) in sensor array 200. The monolithic deviceincluding sensor array 200, processor, and memory can be fabricated as adedicated ASIC. In some embodiments, sensor array 200 can be fabricatedusing 3D stacking technology and can include two or more monolithicdevices, each fabricated on a single substrate and stacked withelectrical connections running between them. The top monolithic devicecan include an array of photosensors 152 and be tuned for optimal lightsensing while the underlying substrate can include a processor andmemory and be optimized for digital logic. In some embodiments, sensorarray 200 can be split into multiple monolithic devices, each optimizedfor sensing a different wavelength (or multiple different wavelengths)of light or optimized for depth sensing vs ambient-light imaging; themonolithic devices may be arranged side-by-side and associated withdifferent channels of the sensor array shown in FIG. 3. In someembodiments, sensor array 200 can also include micro-optical components(e.g., micro-optics 332R/G/B/L and/or channel-specific compensatingmicro-optic elements 370R/G/B) as part of the monolithic structure. Insuch instances, micro-optical components can be formed on the same ASICwith sensor array 200 or fabricated on separate wafer substrates andbonded to the sensor array ASIC at the wafer level so that they becomepart of the monolithic structure with separate substrate layers for eachlayer of the sensor channel. For example, a compensating micro-opticlayer, an aperture layer, a collimating lens layer, an optical filterlayer and a photodetector layer can be stacked and bonded to multipleASICs at the wafer level before dicing. The aperture layer can be formedby laying a non-transparent substrate on top of a transparent substrateor by coating a transparent substrate with an opaque film. In such anembodiment, the dicing step forms multiple ASICs, each with its ownmicro-optic structure bonded directly thereto. As another example, themicro-optical components can be formed as a separate monolithicstructure that can be bonded directly to an ASIC after the ASIC isseparated from a larger wafer via a dicing process. In this manner, theASIC and micro-optic structure can be bonded together to form a singlemonolithic structure. In yet other embodiments one or more components ofsensor array 200 may be external to the monolithic structure. Forexample, aperture layer 310 may be implemented as a separate metal sheetwith pin-holes.

In examples described above, three ambient light channels (tuned forred, green, and blue light respectively) are provided. This is for easeof illustration, and embodiments of the invention are not limited to anyparticular number or combination of ambient light channels. In someembodiments, a sensor row can have fewer than three ambient lightchannels; for instance, a sensor row may have one ambient-light channelwith an optical filter that passes “white light” (e.g., encompassing theentire visible-light spectrum) or with no optical filter (in which casethe spectral selectivity is determined by the sensitivity of thephotosensor). In other embodiments, a sensor row can have more thanthree ambient light channels. By way of illustration, FIG. 4 shows asimplified top view of a sensor array 400 according to an embodiment ofthe present invention that has a larger number of ambient light channelsin each row to provide additional multispectral imaging capability.Again, the number and combination of sensor channels is for purposes ofillustration.

Sensor array 400 includes 64 LIDAR sensor channels 402. In this example,LIDAR sensor channels 402 are arranged in a staggered grid, but thisarrangement is not required. Thirty-two of the 64 LIDAR sensor channelshave an associated row 404 of ambient light sensors 406, but in otherembodiments every LIDAR sensor channel 404 can have an associated row ofambient light sensors 406. In this example, the ambient light sensors406 in each row include eight spectral color channels 410, each definedby a different bandpass filter; two IR-band color channels 412; fourpolarization channels 414; and two ultra-narrow absorption-bandchannels. Each channel can have an internal structure as described abovewith reference to FIG. 1A or 1B, and sensor array 400 can be fabricatedusing techniques described above or other techniques.

Spectral color channels 410 can be created by using appropriate bandpassfilters as optical filter 142. In addition to red, green, and bluechannels, spectral color channels 410 in this example include channelstuned to wavelength ranges corresponding to orange, yellow, cyan,indigo, and violet. Other examples of spectral channels can includeinfrared, ultraviolet, and/or white (e.g., broad spectrum) channels, aswell as channels tuned to any portion of the visible, infrared, orultraviolet light spectrum. In some embodiments, each spectral colorchannel 410 may have a compensating channel-specific micro-optic element(similar to micro-optic elements 370R/G/B in FIG. 3) whose opticalproperties are based at least in part on the wavelength range to whichthe channel is tuned; examples of channel-specific micro-optics aredescribed below.

IR-band color channels 412 can be additional spectral color channelswith bandpass filters tuned to infrared portions of the spectrum. Insome embodiments, it may be desirable to avoid the LIDAR operatingfrequency so that stray LIDAR radiation is not conflated with ambientIR. In some embodiments, each IR-band color channel 412 may have achannel-specific compensating micro-optic element whose opticalproperties are based at least in part on the wavelength range to whichthe channel is tuned.

Polarization channels 414 can be created by using an opticalpolarization filter, such as a grating, instead of or in addition to anoptical bandpass filter 142. The polarization filters in each channel ofgroup 414 can be tuned to a different angle for linearly polarized lightby orienting the polarization filters for different channels atdifferent angles. In one embodiment, four polarization channels 414 haverespective orientations of 0 degrees, 90 degrees, 45 degrees, and 135degrees. Polarization filters may also be tuned to other forms ofpolarization, such as circular and/or spiral polarization. Thepolarization filters may be applied to different surfaces of micro-opticsensor channel 200 in a similar manner to bandpass filters, or they maybe fabricated as a metal grating directly within the metal layers of thephotosensor(s) 152. In some embodiments, each polarization channel 414may have a channel-specific compensating micro-optic element. In somecases, e.g., where polarization channels 414 are not restricted to aparticular wavelength band, compensating micro-optic elements may beomitted or may be tuned to a central wavelength in the band.

Absorption-band channels 416 can each be defined by a narrowband opticalfilter corresponding to an absorption band that is characteristic of aparticular substance of interest. In this case, absence of a signal inthe absorption-band channel can be interpreted (e.g., in conjunctionwith information from other spectral color channels) as indicating thepresence of a substance that absorbs light in that band. For example, insome applications it may be useful to distinguish foliage (e.g., trees,grass, other plants) from other categories of objects (e.g., cars,buildings). Chlorophyll, which is generally associated with foliage, hasmultiple narrow absorption bands in the IR spectrum, and absorption-bandchannels may be tuned to some or all of these bands. As another example,many gases have absorption bands in the shortwave, midwave, and longwaveIR regions, and absorption band channels may be tuned to those bands toidentify gaseous atmospheric contaminants. Because the system alsoprovides distance to objects, in the case of gas absorption detection,this distance information can be used to calculate the distance throughthe atmosphere over which the absorption measurement was taken, whichcan help with determining a confidence level for the detection and/orconcentration of the contaminant. As with other channels, in someembodiments each absorption-band channel 416 may have a channel-specificcompensating micro-optic element whose optical properties are based atleast in part on the band to which the channel is tuned.

These examples of ambient-light sensor channels are illustrative and canbe modified. The qualifier ambient-light, as applied to sensors orsensor channels, should be understood as referring generally to sensorsthat operate to measure the amount (intensity) of incident light havingthe characteristic(s) for which the channel is tuned (e.g., wavelengthrange and/or polarization). Ambient-light sensor channels do not rely onintentional illumination of the field of view (in contrast to the LIDARsensor channels, which are designed to detect intentionally emittedlight); however, intentional illumination (e.g., using an automobileheadlight or camera flash) is not precluded.

A row of a sensor array can include a LIDAR sensor channel (or multipleLIDAR sensor channels, each operating at a different wavelength), plusany number and combination of ambient-light sensor channels, includingone or more visible-light sensor channels tuned to any desired color orrange of colors, one or more polarization sensor channels, one or moreinfrared light sensor channels, one or more ultraviolet light sensorchannels, one or more absorption-band sensor channels, and so on. Asanother example, the ambient-light sensor channels in a given row caninclude two or more sensor channels tuned to the same wavelength rangebut with different attenuation filters, allowing for higher dynamicrange in the image.

Further, it is not required that every LIDAR sensor channel in a sensorarray have an associated row of ambient-light sensor channels or thatevery row of ambient-light sensor channels has an associated LIDARsensor channel. As described below, the arrangement of a LIDAR sensorchannel and a set of ambient light sensor channels in a single row canfacilitate registration between images captured at various wavelengthsand depth data during a scanning operation, but as long as the offsetbetween different sensor channels is fixed and known, interpolation canbe used to generate multispectral image pixels.

1.2.2. Sensor Arrays with Multispectral Sensor Channels

In embodiments described above, each sensor type for a multispectralpixel is provided as a separate sensor channel. It is also possible tocombine multiple sensor types in a single sensor channel. For example, aLIDAR sensor channel may use multiple SPADs as a photosensor, with depthmeasurements based on how many of the SPADs trigger in a given timeinterval. An ambient-light channel may use a single SPAD or standardphotodiode, which occupies a smaller area of a semiconductor device.Accordingly, some embodiments may include one or more “multispectral”sensor channels in a row of sensors.

FIG. 5 shows a simplified top view of a sensor array 500 thatincorporates multispectral sensor channels according to an embodiment ofthe present invention. Sensor array 500 includes 64 LIDAR sensorchannels 502. In this example, LIDAR sensor channels 502 are arranged ina staggered grid, but this arrangement is not required. Thirty-two ofthe 64 LIDAR sensor channels have an associated multispectral sensorchannel 506, but in other embodiments every LIDAR sensor channel 504 canhave an associated multispectral sensor channel 506. In this example, asseen in inset 510, multispectral sensor channel 506 can incorporate ared color sensor 512, a green color sensor 514, a blue color sensor 516,polarization sensors 518, 520, 522, and an IR-band color channel 524.

In some embodiments, each multispectral sensor channel 506 can beimplemented as a single instance of a sensor channel as described abovewith reference to FIG. 1A or 1B. Photosensor layer 150 can include adifferent photosensor 152 for each type of light to be detected. In thiscontext, each photosensor 152 can be, for example, a standard photodiodewith an amplifier, coupled to a capacitive charge bucket and read outusing an analog-to-digital converter (ADC). Alternatively, eachphotosensor 152 can be one or more SPADs with an analog front end and anintegration register to count photons. One or more patterned opticalfilters can be used in optical filter layer 140 to direct light havingdesired properties onto a particular photosensor 152. Each photosensor152 can be separately read out (using appropriate electronics), therebyproviding multiple outputs. The term “multispectral sensor channel” asused herein refers to a configuration where a single optical channelprovides separate data outputs for different photosensors disposedtherein, each of which can be tuned (e.g., via optical filters) todetect light having different characteristics. As can be seen, use ofmultispectral sensor channels can reduce the area consumed by a givenset of sensor types.

It should be understood that the particular number and combination ofsensor types included in a multispectral sensor channel can be variedfrom that shown. For instance, a multispectral sensor channel caninclude any or all of the ambient-light sensor types described above,including visible, ultraviolet, infrared, polarization, wideband, and/ornarrowband sensors. In some embodiments, a row in a sensor array such assensor array 500 can include, in addition to one or more LIDAR sensorchannels (operating at different wavelengths), any number ofmultispectral sensor channels, each incorporating a differentcombination of sensor types. A row in a sensor array such as sensorarray 500 also can include one or more “single-type” ambient-lightsensor channels (such as any of the sensor channels shown in FIG. 4) incombination with one or more multispectral sensor channels.

1.2.3. Sensor Arrays with Hybrid Sensor Channels

In sensor array 500 of FIG. 5, LIDAR (ranging) sensor channels areseparate from the multispectral sensor channels (which measure ambientlight). In other embodiments, a sensor array can include channels thatincorporate both ranging (e.g., LIDAR) sensors and one or moreambient-light sensors. Such channels are referred to herein as “hybridsensor channels” or “hybrid sensor pixels.”

FIG. 6 shows a simplified top view of a sensor array 600 thatincorporates hybrid sensor channels according to an embodiment of thepresent invention. Sensor array 600 includes 128 hybrid sensor channels602 arranged in a rectilinear grid. It is to be understood that thenumber and arrangement of sensor channels can be varied.

As shown in inset 610, each hybrid sensor channel 602 can include a setof LIDAR photosensor elements 650, as well as a number of ambient-lightphotosensors tuned (e.g., using optical filters) to detect light havinga particular property. In this examples, the ambient-light photosensorsinclude a red color sensor 612, an orange color sensor 614, a yellowcolor sensor 616, a green color sensor 618, an ultraviolet color sensor620, a cyan color sensor 622, a violet color sensor 624, a blue colorsensor 626, polarization sensors 628, 630, 632, and an IR-band colorsensor 634. In the example shown, LIDAR photosensor elements 650 occupya central region within the channel area of hybrid sensor channel 602,while the ambient-light photosensors are arranged in a peripheral regionof the channel area surrounding the central region. Other configurationsare also possible.

In some embodiments, similarly to multispectral sensor channels 506,each hybrid sensor channel 602 can be implemented as a single instanceof a sensor channel as described above with reference to FIG. 1A or 1B.Photosensor layer 150 can include a different photosensor 152 (orgrouping of photosensors 152) for each type of light to be detected. Oneor more patterned optical filters can be used in optical filter layer140 to direct light having the desired properties onto a particularphotosensor 152 (or grouping of photosensors 152). Each photosensor 152(or grouping of photosensors 152) can be separately read out usingappropriate electronics, thereby providing multiple outputs.

A “hybrid sensor channel” can be understood as a special case of amultispectral sensor channel that includes photosensors and associatedreadout circuitry configured for determining time of flight ofemitted/reflected light as well as other photosensors and associatedreadout circuitry configured for measuring light intensity. FIG. 7 showsa simplified schematic view of a hybrid sensor channel 602, indicatingthe associated readout circuitry. In this example, each ambient-lightphotosensor 612-634 is implemented using a standard photodiode with anamplifier coupled to a capacitive charge bucket 712-734. Capacitivecharge buckets 712-734 are each connected to multichannel countercircuitry 750, which can determine a count of photons detected (e.g.,during a shutter interval) by each ambient-light photosensor 612-634.

LIDAR photosensor elements 650 in this example can be implemented usingSPADs connected to timing circuitry 760, which is capable of timing thearrival of photons and storing the arrival times in a memory bank ofphotons over time, thereby enabling depth measurements.

As noted above, each hybrid sensor channel 602 can be implemented as asingle instance of sensor channel 100 of FIG. 1A (or sensor channel 100′of FIG. 1B). FIG. 8 is a simplified schematic side view of a portion ofsensor array 600 showing the channel structure. Each hybrid sensorchannel 602 has an aperture 812 (in aperture layer 810), optical layer830, filter layer 840, and photosensor layer 850 (shown in oblique viewfor clarity of illustration). Filter layer 840 can include patternedfilters 842 (shown in oblique view for clarity of illustration), whichcan be located on the filter wafer or directly deposited on thephotosensor ASIC on top of the appropriate photosensor elements.

In operation, light 860 is directed into aperture 812 and propagatesthrough channel 602 as shown by arrows 862. Patterned filters 842 directlight having desired properties onto individual photosensors 852 inphotosensor layer 850. As described above, the appropriate readoutelectronics can be used to extract time-of-arrival information from theLIDAR photosensors, as well as accumulated photon counts in color,polarization, and/or other ambient-light photosensors.

It should be understood that the particular number and combination ofsensor types included in a hybrid sensor channel can be varied from thatshown. For instance, a hybrid sensor channel can include, in addition toLIDAR sensors, any or all of the ambient-light sensor types describedabove, including visible, ultraviolet, infrared, polarization, wideband,and/or narrowband sensors. Further, while sensor array 600 is shown as a2D array of identical sensor channels 602, this is not required. Hybridsensor channels could be included in a 1D array or in a row with othersensor types similarly to sensor array 400 of FIG. 4 or sensor array 500of FIG. 5. The arrangement and configuration of sensor channels can bevaried as desired.

1.2.4. Dual-Plane Multispectral Sensor Arrays

In embodiments described above, it is assumed that the photosensors forvarious channel types are arranged in one plane. In other embodiments,different photosensors can be in different planes.

By way of example, FIG. 9 shows a simplified side cross-section view ofa portion of another embodiment of a sensor array 900. Sensor array 900includes one or more LIDAR channels 902, each of which can be a separateinstance of sensor channel 100 of FIG. 1A (or sensor channel 100′ ofFIG. 1B). LIDAR channel 902 is fabricated on an ASIC 904, which includesone or more photosensors 906 for each LIDAR channel 902. An aperturelayer 910 overlies LIDAR channels 902 and has an aperture 912 formedtherein to direct light into each LIDAR channel 902. In these respects,sensor array 900 can be similar to other embodiments described above.

In this example, aperture layer 910 is a second ASIC that hasphotosensors 916R, 916G, 916B fabricated or otherwise disposed in or onits top surface, in locations that do not obstruct aperture 912.Photosensors 916R/G/B are located in the same plane as aperture 912,which can be the focal plane of a bulk imaging optic for the sensorarray. Color filters 918R, 918G, 918B, each of which can be a bandpassfilter admitting light within a different wavelength band (red, green,and blue in this example), are placed over photosensors 916R, 916B,916G. This arrangement provides ambient-light sensor channels 920R,920G, 920B. Aperture layer 910 can be electrically connected to readoutand/or control circuitry (e.g., a processor and memory) located in ASIC904, as indicated schematically by wire bond 922. (It should beunderstood that wire-bonding is not required; other techniques forestablishing electrical connections between ASICs can be substituted, orthe two ASICs can each be connected to readout and control circuitrylocated on another device.)

FIG. 10 shows a simplified top view of sensor array 900. Sensor array900 provides a 2D array of multispectral pixels 1020. The size anddimension of sensor array 900 can be varied as desired. As shown ininset 1010, each multispectral pixel 1020 can include a LIDAR sensorchannel 902 and one or more ambient-light sensor channels 920.Ambient-light sensor channels 920 can be fabricated in an ASIC thatoverlies and provides an aperture for LIDAR sensor channel 902 (as shownin FIG. 9). Any number and combination of ambient-light sensor channels920 can be provided, including any of the specific channel typesdescribed above (e.g., color channels, including infrared,visible-light, and/or ultraviolet channels; polarization channels;narrowband absorption channels; and so on).

In some embodiments, aperture-layer ASIC 910 can have a significantlyhigher density of photosensors (or channels) 920 than the “base” ASIC904 that supports LIDAR sensor channels 902. For instance, the LIDARsensor channels may have spacing of 100-400 μm and apertures of 30 μm indiameter. The sensor channels (photosensors or pixels) in aperture layerASIC 910 can be significantly smaller (e.g., in the 1-10 μm size range),meaning that each hybrid pixel 1020 can include a large number ofambient-light pixels. This can allow for a larger number of sensor typesper multispectral pixel and/or multispectral pixels that have higherresolution in the ambient-light imaging channels than in the LIDARchannels.

Multispectral images obtained using aperture layer ASIC 910 may includegaps corresponding to the locations of apertures 912 or LIDAR channels902. In some embodiments, interpolation can be used to fill the gaps.

1.2.5. Multispectral Pixels with Encoded Spectrally-Selective Passbands

In examples described above, different ambient-light sensor channels mayinclude optical filters with different passbands. In some embodiments,the passbands for different ambient-light sensor channels may begenerally non-overlapping so that different ambient-light sensorchannels sample different portions of the optical spectrum (includinginfrared, visible, and/or ultraviolet light). FIG. 11 shows an exampleof non-overlapping passbands for three filters that can be used toprovide ambient-light intensity measurements in some embodiments, e.g.,in the multispectral sensor array of FIG. 2. In this example, a “blue”(B) filter 1102 has a passband from about 425 nm to about 515 nm; a“green” filter (G) 1104 has a passband from about 515 nm to about 610nm, and a “red” (R) filter 1106 has a passband from about 610 nm toabout 700 nm. It is to be understood that these ranges and boundariesare illustrative and can be varied. In some embodiments, the passbandsof different filters may have some overlap. For instance, B filter 1102might have a passband from about 410 nm to about 510 nm while G filter1104 has a passband from about 490 nm to about 620 nm and R filter 1106has a passband from about 600 nm to about 700 nm. As another example, Bfilter 1102 might have a passband from about 410 nm to about 440 nmwhile G filter 1104 has a passband from about 490 nm to about 620 nm andR filter 1106 has a passband from about 600 nm to about 700 nm. Othervariations are also possible. The filter set shown in FIG. 11 canprovide “R,” “G,” and “B” spectral intensity measurements for amultispectral pixel. (The names R, G, and B are used here as suggestiveof red, green, and blue, but the passbands of filters having these namesneed not correspond to passbands associated with any particular color.)

In some embodiments, different ambient-light sensor channels may haveoverlapping passbands that are selected to encode spectral information.FIG. 12 shows an example of overlapping passbands for three filters thatcan be used to provide ambient-light intensity measurements with encodedspectral information in some embodiments. In this example a first filter1202 has a “W” passband that encompasses roughly the entirevisible-light spectrum (wavelengths from about 425 nm to about 700 nm).A second filter 1204 has a “Cb” passband from about 425 nm to about 610nm, and a third filter 1204 has a “Cr” passband from about 515 nm toabout 700 nm. Intensity measurements from ambient-light sensor channelshaving the passbands shown in FIG. 12 can be used to extract R, G, and Bspectral information corresponding to the spectral measurements from thefilter set of FIG. 11. For example, if the intensity measurements fromfilters 1202, 1204, and 1206 are denoted as W, Cb, and Cr, respectively,then intensity in the R, G, and B bands identified in FIG. 11 can becomputed as:R=W−Cb  (1a)B=W−Cr  (1b)G=W−(R+B)=Cb+Cr−W  (1c)These computations can be implemented, e.g., using arithmetic logiccircuits of conventional design, which can be fabricated on the sameASIC as the sensor array.

In this manner, either the non-overlapping filter set of FIG. 11 or thespectrally-encoded filter set of FIG. 12 can provide equivalent spectralinformation. The encoding scheme of FIG. 12 allows each channel toaccept more light, which may improve measurement accuracy.

The filter set of FIG. 12 can be incorporated into various multispectralsensor arrays. FIG. 13 shows a simplified front view of a sensor array1300 according to some embodiments. Sensor array 1300 can be similar tosensor array 200 of FIG. 2 and can include LIDAR sensor channels 202 (asdescribed above), each of which can be associated with a row 1304 thatincludes ambient-light sensor channels 1306 a (W passband), 1306 b (Cbpassband), and 1306 c (Cr passband), where the W, Cb, and Cr passbandsare defined as shown in FIG. 12. Sensor data from ambient-light sensorchannels 1306 a, 1306 b, 1306 c of a given row 1304 can be provided toan on-chip arithmetic logic circuit 1310 that implements Eqs. (1a)-(1c)to produce R, G, and B output signals. It should be understood that thesensor rows 1304 can also include other types of ambient-light sensorchannels, e.g., as described above with reference to FIG. 4.

Spectrally-encoded passbands can also be implemented in sensor arrayshaving multispectral sensor channels or hybrid sensor channels. FIG. 14Ashows a simplified front view of a multispectral sensor channel 1400according to some embodiments. Multispectral sensor channel 1400 has apatterned optical filter that includes regions 1402 having a W passband(as shown in FIG. 12), regions 1404 having a Cb passband, and regions1406 having a Cr passband. In this example, the regions are square, butno particular filter geometry is required. A separate photosensor (e.g.,one or more SPADs) can be placed behind each region, as described abovewith reference to FIG. 5. While FIG. 14A shows three regions for eachpassband, it is to be understood that any number of regions can beprovided for a given passband (as long as a separate photosensor isprovided for each region).

All photosensors associated with the same passband can provideambient-light intensity measurements (e.g., in the form of electronicsignals representing photon counts) to the same integration register.Thus, for example, register 1412 can accumulate (or integrate) photoncounts from photosensors in regions 1402, register 1414 can accumulatephoton counts from photosensors in regions 1404, and register 1416 canaccumulate photon counts from photosensors in regions 1406. Registers1412, 1414, and 1416 can provide accumulated photon counts as inputs toan on-chip arithmetic logic circuit 1420 that implements Eqs. (1a)-(1c)to produce R, G, and B output signals. It should be understood thatmultispectral sensor channel 1400 can also include other regions havingdifferent types of optical filters, e.g., as described above withreference to FIG. 5. Further, while FIG. 14A shows optical filters withthe same passband occupying contiguous regions within the channel area,this is not required. For example, FIG. 14B shows an alternativepatterned optical filter 1400′ in which regions 1402, 1404, 1406 havingthe same passband are distributed across the channel area, which mayfurther improve measurement accuracy. As in FIG. 14A, intensitymeasurements (e.g., photon counts) from different photosensorsassociated with the same type of optical filter can be accumulated (orintegrated) in the same integration register.

The foregoing examples of optical filters with spectrally-encodedpassbands and ambient-light sensor channels incorporating such filtersare illustrative and not limiting. Spectrally-encoded passbands can beincorporated into any of the multispectral sensor arrays describedabove, including 1D arrays, 2D arrays, arrays with multispectral pixels,and arrays with hybrid pixels. Examples herein use three passbands toencode three color channels, but it will be appreciated that any numberof different optical filters having overlapping passbands can be used toencode spectral information with any granularity desired. This encodingtechnique is not limited to spectral characteristics of light. Forinstance, similar arrangements can be implemented using polarizationfilters (e.g., in combination with a non-polarizing filter) to encodepolarization information with any granularity desired.

It should be understood that the multispectral sensor arrays describedabove are illustrative and that many variations and modifications arepossible. A given multispectral sensor array can include any combinationof depth channels (e.g., LIDAR sensor channels or hybrid sensorchannels), ambient-light sensor channels, multispectral sensor channels,and/or hybrid sensor channels, which can be constructed using any of thetechniques described above or other techniques. Components describedwith reference to one example or embodiment may be used in otherembodiments.

2. Optics for Multispectral Sensor Arrays

Various sensor arrays described above operate in response to light thatpasses through an aperture associated with each channel. In someembodiments, optical systems are provided to direct and focus light ontothe aperture plane. Examples of optical systems and optical elementsthat can be used in connection with multispectral sensor arrays (e.g.,sensor arrays 200, 400, 500, 600, and/or 900) will now be described.

As used herein, the term bulk optic(s) refers to single lenses and/orlens assemblies that have a focal plane and transmit light from or toall micro-optic channels in an array simultaneously. In someembodiments, bulk optics may have sizes (e.g., diameters) on the orderof millimeters or centimeters or greater, such as those used incommercially available camera lenses and microscope lenses. In thisdisclosure, the term bulk optics is contrasted with the termmicro-optics which refers to optical elements or arrays of opticalelements that are provided for a specific sensor channel. In someembodiments, micro-optics may have individual element diameterscorresponding to the size of a single sensor channel (e.g., on the orderof a few micrometers to a few millimeters in size or smaller). Ingeneral, micro-optics can modify light differently for differentemitters and/or different sensor channels of an array of emitters or anarray of sensor channels, whereas the bulk optics modify light for theentire array.

2.1. Bulk Optical Modules

A multispectral sensor array (such as any of the sensor arrays describedabove) can be incorporated into a light ranging/imaging device 1500 asshown in FIG. 15. Light ranging/imaging device 1500 includes a lighttransmission (Tx) module 1510 and a light sensing (Rx) module 1540,which can include an implementation of sensor array 200 (or any othersensor array described above). Additional examples of configurations forlight transmission module 1510 and light sensing module 1540 are setforth in U.S. application Ser. No. 15/979,235 entitled “Optical ImagingTransmitter with Brightness Enhancement,” filed on May 14, 2018, andU.S. application Ser. No. 15/979,266 entitled “Spinning LIDAR Unit withMicro-optics Aligned behind Stationary Window,” filed on May 14, 2018,the disclosures of each of which are incorporated herein by reference intheir entirety for all purposes.

As shown in FIG. 15, Tx module 1510 can include a Tx-side micro-opticspackage 1520 and a bulk optical element 1530. Tx-side micro-opticspackage 1520 includes a number of light emitters 1522, and optionallyincludes a micro-lens layer 1524 and an aperture layer 1526. Emitters1522 can be arranged in a one or two-dimensional array of transmitterchannels, e.g., channel 1525 shown in the boxed region. Each one of thetransmitter channels has one or more light emitters 1522, e.g.,near-infrared (NIR) vertical cavity semiconductor lasers (VCSELs) or thelike, capable of emitting narrowband light, and optionally, a micro-lensfrom lens layer 1524 and an aperture from aperture layer 1526.

In operation, Tx module 1510 provides active illumination of objects inthe area around the LIDAR system by, e.g., transmitting pulses of narrowband light, e.g., NIR light having a spectral width of, e.g., 10 nm, 2nm, 1 nm, 0.5 nm, 0.25 nm or less, into one or more fields of view. Rxmodule 1540, particularly LIDAR sensor channels 202 thereof, detectsreflected portions of the transmitted narrowband light that is reflectedby the objects in the scene. At the same time, each ambient-lightsensing channel 206R/G/B of Rx module 1540 can detect ambient light inits particular wavelength band.

Light emitted from each one of the transmitters diverges as itapproaches one of the micro-optics of the Tx-side micro-optic lens layer1524. Micro-lenses from micro-lens layer 1524 capture the diverginglight and refocus it to a focal plane that is coincident with aperturesin aperture layer 1526 that includes an array of apertures thatcorrespond in position to the array of micro-optics and the array ofemitters. Aperture array 1526 can reduce crosstalk in the system. Afterexiting the micro-lenses, the focused light again diverges in the formof cones that then encounter the Tx-side bulk imaging optics module1530. In some embodiments, the separation between the micro-lens layer1524 and the Tx-side bulk imaging optics module 1530 is equal to the sumof their focal lengths, such that light focused at the aperture array1526 appears as collimated light at the output of the Tx-side bulkimaging optics module 1530 with each collimated bundle of rays exitingthe Tx-side bulk imaging optics module 1530 with a different chief rayangle. Accordingly, the light from each emitter is directed to adifferent field of view ahead of the device. In some embodiments, theTx-side bulk imaging optic 1530 is telecentric on the imaging side(which is the emitter side) of the lens, i.e., the chief rays on theimage side of bulk imaging optic 1530 are substantially parallel to eachother and normal to the image plane (which is the emitter plane) forevery position on the image plane. In this configuration the emitterarray advantageously operates as a telecentric source, i.e., the opticscapture substantially all light produced by the emitter array, evenlight that is emitted from the emitters on the outer edges of the array.Without the telecentric design, light captured by the outer emitters maybe reduced because only the fraction of the emitted ray cone thatcoincides with the lens's oblique ray cone would be captured by thelens. LIDAR sensing channels 202 of Rx module 1540 can be arranged tomatch Tx-side micro-optics package 1520, with a LIDAR sensor channel 202corresponding to each micro-optic transmitter channel 1525.

Rx module 1540 includes an Rx-side bulk imaging optics module 1560 andsensor array 200. The portions of the emitted light that reflect off ofobjects in the field, shown as light rays 1505, enter the Rx-side bulkimaging optics module 1560 from multiple directions. The Rx-side bulkimaging optics module 1560 can include a single lens or a multi-lensgroup that focuses light rays 1505 at a plane that is coincident withthe Rx-side input aperture layer 310, allowing the light to enter theLIDAR sensor channels 202. In some embodiments, Rx module 1540 includesa LIDAR sensor channel for each emitter 1522 with the field of view ofeach individual LIDAR sensor channel 202 matching the field of view ofits respective emitter 1522.

Rx-side bulk imaging optics module 1560 can also collect ambient light.As used herein, “ambient” light refers to any light rays that may bepropagating in the environment and that did not originate from Tx module1510. Ambient light can include direct light from any light source thathappens to be present in the environment (e.g., the sun, an artificialluminaire, a traffic signal, etc.) as well as light that has beenreflected or scattered by an object in the environment (e.g., lightreflected off a road sign, a vehicle, a road surface, a tree, etc.).Ambient light can propagate in any direction, and ambient light thathappens to be propagating in a similar direction to light rays 1505 mayenter and pass through Rx-side bulk imaging optics module 1560.

2.2. Per-Channel Compensating Micro-Optics

In some embodiments, Rx-side bulk imaging optics module 1560 can bedesigned as a monochromatic lens (single lens or lens group) that isoptimized to focus a particular narrow wavelength band, e.g., the LIDARoperating wavelength onto a target plane, e.g., input aperture plane310. Rx-side bulk imaging optics module 1560 may exhibit chromaticaberration (i.e., a focal length that is wavelength-dependent). This mayreduce the collection efficiency of the ambient-light sensor channels:if an implementation of Rx-side bulk imaging optics module 1560 that haschromatic aberration focuses light of the LIDAR operating wavelengthonto input aperture plane 310, then light of wavelengths other than theLIDAR operating wavelength would not focus at input aperture layer 310,and some of that light would be blocked by the aperture stops ratherthan entering ambient light sensor channels 206R/G/B. Further, theamount of light lost due to this effect would be wavelength-dependent,which may complicate analysis of imaging data. In addition, the spatialresolution of these channels would be reduced (field of view would belarger and less well defined, i.e., “blurry”) because the apertures 310are not at the focal plane for their wavelength band or because themonochromatic lens is incapable of providing small focused spots forout-of-band light.

Accordingly, some embodiments of sensor array 200 (or othermultispectral sensor arrays described herein) include channel-specificcompensating micro-optics that can be placed in front of the inputaperture plane to allow more efficient light capture. FIG. 16 is asimplified cross-sectional view of a portion of sensor array 200, withannotations to illustrate the behavior of incident light. (In thisexample, the tapering of the apertures is reversed relative to FIG. 3,so that apertures 312R/G/B/L are shown at bottom surface 360 of aperturelayer 310. However, the same principles apply regardless of the exactlocation of the aperture plane.)

In the example of FIG. 16, the dashed lines illustrate an effect ofchromatic aberration. The converging dashed lines over channels 206R,206G, and 206B show the respective marginal rays for red, green, andblue light rays that have been focused by a bulk optic (e.g., Rx-sidebulk imaging optics module 1560 of FIG. 15) that has chromaticaberration. As can be seen, LIDAR light rays 1620L converge at apertureplane 360; however, light of shorter wavelengths (visible light in thisexample) converges in front of aperture plane 360, with the distancedepending on wavelength. Thus, in this example, focal point 1612R forred light is slightly in front of input aperture 312R, focal point 1612Gfor green light is farther in front of input aperture 312G, and focalpoint 1612B for blue light is farther still in front of input aperture312B. In the absence of corrective optics, the focused red, green, andblue rays (dashed lines) would diverge prior to reaching aperture plane360, leading to varying degrees of light loss at apertures 312R, 312G,and 312B.

In some embodiments, channel-specific compensating micro-optics can beused to correct for such effects. For example, as shown in FIG. 16, afirst compensating micro-optic, in this example a first plano-concavelens 1650R, is placed in front of aperture layer 310, aligned with theopening 362R for red channel 206R. Plano-concave lens 1650R has anoptical prescription (e.g., surface curvature or focal length) thatreduces the divergence of incident light, shifting the focal point forred light from uncorrected focal point 1612R to aperture 312R. A secondcompensating micro-optic, in this example a second plano-concave lens1650G, is aligned with opening 362G. Plano-concave lens 1650G has aprescription that reduces the divergence of incident light more stronglythan plano-concave lens 1650R, shifting the focal point for green lightfrom uncorrected focal point 1612G to aperture 312G. A thirdcompensating micro-optic, in this example a third plano-concave lens1650B, is aligned with opening 362B. Plano-concave lens 1650B has aprescription that reduces the divergence of incident light more stronglythan plano-concave lens 1650G, shifting the focal point for blue lightfrom uncorrected focal point 1612B to aperture 312B. It should beunderstood that each of plano-concave lenses 1650R, 1650G, 1650B in thisexample has a different prescription that is optimized for thewavelength (or wavelength range) that the corresponding sensor channel206R, 206G, 206B is tuned to detect. In this example, no compensatingmicro-optic is provided for LIDAR channel 202 because Rx-side bulkimaging module 1560 already focuses light of the LIDAR operatingwavelength into aperture 312L.

In other embodiments, the particular wavelength for which the Rx-sidebulk imaging module focuses light onto the input aperture plane can bedifferent. By way of illustration, FIG. 17 shows an example ofchannel-specific compensating micro-optics for an embodiment where anRx-side bulk imaging module 1560 that has chromatic aberration focusesblue light onto aperture plane 360. In this example, blue channel 202Bdoes not use any compensating micro-optic, but (due to chromaticaberration) without compensating micro-optics, the focal points for thedesired light wavelengths for other channels would lie beyond apertureplane 360, again leading to wavelength-dependent amounts of light lossand spatial selectivity. To compensate for this, channel-specificcompensating micro-optics, in this example plano-convex lenses 1750R,1750G, and 1750L, can be placed in front of the channel openings for redchannel 206R, green channel 206G, and LIDAR channel 202. In thisexample, the plano-convex lenses have prescriptions that increase thedivergence of incident light, shifting the focal point in a directiontoward aperture plane 360 so that, for a given senor channel, the focalpoint for light of the color to which that sensor channel is tunedcoincides with aperture plane 360. As in the previous example, thechannel-specific compensating micro-optic for each channel has adifferent prescription that brings the focal point for the particularchannel onto aperture plane 360.

In the examples of FIGS. 16 and 17, light is focused onto the apertureplane, then collimated by optical elements within the sensor channel(e.g., as shown in FIG. 1A or 1B). Another option is to providechannel-specific compensating micro-optic elements for the ambient lightchannels that collimate light at the channel-specific wavelength. FIG.18 shows an example of a sensor array 1800 with collimatingchannel-specific compensating micro-optics that can be used in someembodiments. In this example, substrate array 1800 is generally similarto substrate array 200, but the aperture 1812R, 1812G, 1812B for eachambient-light channel is substantially as wide as the channel. (Aperture1812L for LIDAR channel 1802 can be narrower, e.g., as shown.) In thisarrangement, optical element 132 (shown in FIG. 1A or 1B) can beomitted, at least for ambient light channels 1806R, 1806G, 1806B, whichare otherwise similar to ambient light channels 206R, 206G, 206Bdescribed above. It should be noted that with this arrangement,ambient-light channels 1806R, 1806G, 1806B can be made smaller andpacked more tightly than LIDAR channels 1802. In the ambient lightchannels, the narrow channel width can provide spatial selectivitywithout requiring an aperture narrower than the channel width; however,the collimation angle would be larger, which results in increasing thelower bound on the width of a bandpass filter.

Similarly to the example of FIG. 16, Rx-side bulk imaging module 1560focuses light of the LIDAR operating wavelength (rays 1822L) intoaperture 1812L. Light of shorter wavelengths is focused at differentdistances from back plane 1814, as shown by dashed lines. Plano-convexlenses 1850R, 1850G, 1850B decrease the divergence of red, green andblue light, respectively, to collimate the light of desired wavelengthas it enters the channel, as shown by the colored lines. As in theprevious example, the channel-specific compensating micro-optic fordifferent color channels has a different prescription that compensatesfor the wavelength-dependent focal lengths of incoming light.

These examples are illustrative and not limiting. An Rx-side bulkimaging module that has chromatic aberration can be adapted to focuslight of any desired wavelength onto the aperture plane, and channelsthat are sensitive to other wavelengths can have compensatingmicro-optics with wavelength-specific (or channel-specific) positive(focusing) or negative (defocusing) prescriptions placed in front oftheir apertures. For ease of assembly, the compensating micro-opticelements for all channels in the sensor array (or all channels thatinclude such elements) can be placed on the same plane (e.g., on top ofthe aperture layer). The particular shape of the compensatingmicro-optic elements can be varied; for instance, the compensatingmicro-optic for a given channel can include a plano-convex lens, aplano-concave lens, a biconvex lens, a biconcave lens, a convex-concavelens, freeform lenses, or a combination of multiple lenses. Differentshapes can be used for different channel types as desired. As theexamples above show, compensating micro-optics need not be provided forall sensor channels in a given sensor array; in some embodiments, theRx-side bulk imaging module can be designed such that light having thedesired wavelength for one of the sensor channel types is focused at theaperture for the channel. However, no particular design for the Rx-sidebulk imaging module is required, and in some embodiments every sensorchannel may have a channel-specific compensating micro-optic element tocompensate for any aberrations in the system, for instance if the systemcontains a window or housing with optical power that requirescorrection. A sensor array can include multiple sensor channelsassociated with a given wavelength, e.g., as described above. In someembodiments, different sensor channels of the same channel type (e.g.,wavelength range) can be designed identically so that the compensatingmicro-optic prescription needs to be determined only once per channeltype. Alternatively, since different channels are in different locationsrelative to the Rx-side bulk imaging module and since aberration effects(including chromatic aberration) in an optical module can depend ondistance from the optical axis of the module, it may be desirable todesign a compensating micro-optic for each channel individually. In anycase, an appropriate prescription for a given channel-specificcompensating micro-optic element can be determined by applyingconventional optical modeling techniques to a particular channel designand a particular design of the Rx-side bulk imaging module.

Channel-specific compensating micro-optics can be fabricated from anymaterial that is optically transparent at the relevant wavelengths.Molding or other processes can be used to shape the micro-optics. Insome embodiments, the micro-optics for all channels of the sensor arraycan be fabricated as a single structure having surface features (e.g.,regions of locally convex or concave curvature) that define theper-channel micro-optic element and assembled with other layers of amonolithic sensor array. Further, the prescriptions for thechannel-specific micro-optic elements can be chosen based on any opticalproperties of the bulk optics, not limited to chromatic aberration.Examples of using channel-specific micro-optic elements to compensatefor focal plane curvature of a bulk optic are described below.

2.3. Achromatic Bulk Optics

In some embodiments, per-channel compensating micro-optics can beomitted. For example, the bulk optical module may have negligible (orno) chromatic aberration so that light of all relevant wavelengths isfocused at the same aperture plane. An achromatic bulk optic module maybe particularly useful for sensor arrays that include multispectralsensor channels (e.g., sensor array 500) and/or hybrid sensor channels(e.g., sensor array 600), as well as for sensor arrays where some of thephotosensors are disposed in the aperture plane (e.g., sensor array900).

FIG. 19 shows an example of sensor array 200 in a system with anachromatic bulk optical module that focuses all colors in aperture plane310. Per-channel compensating micro-optics are not used in this example.For channels with wide passband (e.g., channels 206R/G/B), the opticalfilters can be located anywhere in the channel. For polarizationchannels (not shown), one or more polarization gratings can be includedin the stack (e.g., in the optical filter layer) or in a metal layer ofthe underlying ASIC photosensor(s).

FIG. 20 shows another example of a sensor array 2000 in a system with anachromatic bulk optical module that focuses all colors in aperture plane2010. In this example, LIDAR sensor channel 2002 and ambient-lightsensor channels 2004R, 2004G, 2004B are fabricated as separatemonolithic devices arranged side-by-side. Each sensor channel 2002,2004R/G/B has an aperture 2012L, 2012R/G/B located in the same apertureplane 2010. LIDAR sensor channel 2002 includes collimating optics 2020.Ambient-light sensor channels 2004R/G/B in this example do not includecollimating optics. Instead, non-refractive optics (e.g., light guides)can be used to direct light through the channel to photosensors 2030R,2030G, 2030B. For wide passbands, color filters can be placed anywherein the channel. Although shown for sensor channels having a singlesensor type, channel configurations with non-refractive optics may alsobe useful for multispectral sensor channels (e.g., multispectral sensorchannels 506 of FIG. 5) or hybrid sensor channels (e.g., hybrid sensorchannels 602 of FIG. 6).

2.4. Micro-optics to Compensate for Focal Plane Curvature

Examples described above assume that the bulk optical module focuseslight (of a given wavelength) onto a (flat) image plane, regardless ofwhere the light passes through the bulk optical module. In the examplesshown above (e.g., in FIGS. 19 and 20), the image plane coincides withthe aperture plane.

In some embodiments, a bulk optical module may focus light of a givenwavelength onto a curved surface (referred to as a “curved focal plane”)rather than a flat plane. Where this is the case, per-channelmicro-optics similar to examples described above can be employed tocompensate for an offset between the curved focal plane and the (flat)aperture plane at the location of each aperture. FIG. 21 shows anexample of per-channel micro-optics to correct for focal length of abulk optic module that can be used in some embodiments. A sensor array2100 has a row of sensor channels 2102 arranged in a plane. (Aone-dimensional sensor array is shown for simplicity of illustration; itwill be understood that the same principle applies to two-dimensionalsensor arrays.) A planar aperture layer 2104 has apertures 2106 arrangedsuch that each aperture 2106 passes light to a corresponding sensorchannel 2102. In this example, bulk optic module 2108 has a curved focalplane, represented by dotted line 2110. In front of each aperture 2106is a channel-specific micro-optic element 2112 that compensates for thecurvature of focal plane 2110. For instance, each channel-specificmicro-optic element 2112 can have a prescription that corrects for theoffset between the location of the corresponding aperture 2106 and acorresponding location on curved focal plane 2110 so that light isfocused into the corresponding aperture 2106 (rather than in front of orbehind aperture 2106). In this example, for most of apertures 2106, thecorresponding location on curved focal plane 2110 is in front of planaraperture layer 2104, and the corresponding channel-specific micro-opticelements 2112 have positive focusing power. In this example, themagnitude of the focusing power of different channel-specificmicro-optic elements 2112 increases with radial distance r from theoptical axis 2114 of bulk optic module 2108. In other examples (notshown) curved focal plane 2110 can be behind planar aperture layer 2104at some or all of the aperture locations 2106, and any particularchannel-specific micro-optic element 2112 can have positive or negativefocusing power as needed. In some embodiments, curved focal plane 2110of bulk optic module 2108 may coincide with the aperture plane of one ormore sensor channels, and channel-specific micro-optic elements 2112 forsuch sensor channels may be omitted, or micro-optic elements with zerofocusing power may be provided.

FIG. 22 shows another example of a receive (Rx) module 2200 withchannel-specific micro-optic elements. Rx module 2200 can be similar toRx module 1540 of FIG. 15 described above and can include anycombination of sensor channel types. For instance, all channels 2202 canbe LIDAR sensor channels, all channels can be ambient-light sensorchannels, all channels 2202 can be hybrid sensor channels, or acombination of different sensor channel types can be present. In thisexample, channel-specific micro-optic elements 2204 are provided infront of an aperture plane 2206 to compensate for the curvature of thefocal plane of bulk optic module 2208. As in the example of FIG. 21, theprescription of channel-specific micro-optic elements 2204 can be afunction of the radial distance from the optical axis, corresponding tothe curvature of the focal plane of bulk optic module 2208. In thisexample, channel-specific micro-optic elements 2204 have positivefocusing power that increases with radial distance from the opticalaxis; however, as noted above, some or all channel-specific micro-opticelements 2204 can have negative or zero focusing power.

In some embodiments, channel-specific micro-optic elements that correctfor focal length can be used in LIDAR transmitter arrays as well as insensor arrays. FIG. 23 shows an example of a transmit (Tx) module 2300with channel-specific micro-optic elements. Tx module 2300 can besimilar to Tx module 1510 of FIG. 15 described above and can include a1D or 2D array of emitter channels 2302. In this example,channel-specific micro-optic elements 2304 are provided to compensatefor the curvature of the focal plane of bulk optic module 2308. As inthe examples of FIGS. 21 and 22, the prescription of channel-specificmicro-optic elements 2304 can be a function of the radial distance fromthe optical axis, corresponding to the curvature of the focal plane ofbulk optic module 2308.

These examples are illustrative and not limiting. For instance, in theexamples described above, the prescription (focusing power) of thechannel-specific micro-optic elements is varied to compensate for focalplane curvature of the bulk optic. In other embodiments, a similarper-channel compensation can be achieved by using channel-specificmicro-optic elements with the same prescription and a variable standoffdistance between the channel-specific micro-optic element and theaperture plane; the standoff distance can be based on the radialdistance from the optical axis. A combination of varying theprescription and the standoff distance can also be used.

It should be understood that channel-specific micro-optic elements thatcompensate for focal plane curvature of a bulk optic module can beuseful in contexts other than multispectral sensor arrays. For instance,a LIDAR system that does not include ambient-light sensor channels mayalso benefit from the clearer imaging associated with compensation forfocal plane curvature of the bulk optic modules. Channel-specificmicro-optic elements can be incorporated into the transmitter module,the receiver module, or both, depending on the properties of the bulkoptics provided for each module. Imaging systems with only ambient-lightsensor channels may also benefit, and presence of a transmit module isnot required. Use of channel-specific micro-optic elements to compensatefor focal plane curvature of a bulk optic module may allow reduction incost and/or size of the bulk optic module, since bulk lens systemswithout focal plane curvature are generally larger and more complex thanbulk lens systems with focal plane curvature.

In some embodiments of multispectral sensor arrays (e.g., any of theexamples described above) or other systems where the bulk optic moduleexhibits chromatic aberration as well as focal plane curvature, thechannel-specific micro-optic element for any given channel can bedesigned to compensate for both effects, so that light of the desiredwavelength for a given channel is focused onto the aperture plane. Moregenerally, channel-specific micro-optic elements can have prescriptionsdesigned to compensate for any optical property (or opticalcharacteristic) of a bulk optic module that has different effects forchannels at different positions within an array.

2.5. Uniform Sampling of Object Space

Sensor arrays of the kind described herein can be incorporated into avariety of ranging/imaging systems that generate images made up ofmultispectral image pixels that each include data obtained from sensorsof different types. It is often desirable that such images represent auniform sampling of the sensor system's field of view (also referred toas “object space”). Specifically, it is desirable to define a regular“grid” of sampling areas in object space (referred to herein as“object-space pixels”), which may be arranged in rows and columns, andto design the sensor system and its operation to produce a grid of imagepixels, each of which corresponds to a single object space pixel asimaged by each sensor type in the sensor array. In some embodiments of aranging/imaging system, the bulk optics are designed to support thisuniform sampling of object space.

2.5.1. Optics for Static Systems

In some embodiments, multispectral sensor arrays of the kind describedabove may be used in a “static” ranging/imaging system. Such a systemincorporates a 2D sensor array (e.g., sensor array 600 or sensor array900 described above) and acquires an image over the surface of thesensor array without moving the array, as described below. An imagepixel in such a system can correspond to a hybrid sensor channel (e.g.,hybrid sensor channel 602) or a multispectral pixel (e.g., multispectralpixel 1020). Such arrays can uniformly sample the object space, providedthat the bulk imaging optic is free of localized distortion. In someembodiments, use of a flat-field focal-length distortion profile may bedesirable, so that light is focused onto the aperture plane across theentire array.

2.5.2. Optics for Scanning Systems

In some embodiments, multispectral sensor arrays of the kind describedabove may be used in an angular scanning or rotating mode such thatdifferent sensor channels in a row of a sensor array successively image(i.e., sense photons from) a particular region in the field of view.Examples of scanning operations are described below. For purposes ofthis description, it is assumed that, during a scanning operation, thesensor system rotates about an axis that is transverse to the rows andthat the sensor channels are operated as the sensor system rotatesthrough different angles. (It should be understood that scanningbehavior can also be achieved without moving the sensor array, e.g., byusing a MEMS mirror to reflect light from different areas of objectspace onto the array at different times.) It is also assumed that thesensor array and the bulk optical module are held in fixed relation toeach other in the sensor system, so that a given sensor channel has afixed spatial relationship to the optical axis of the bulk imaging opticand “sees” through the same portion of the bulk optical module,regardless of orientation of the system in space.

To simplify image analysis, it is generally desirable that a scanningsensor system uniformly samples the object space. In this context, thegrid of object-space pixels is considered to be arranged with rows alongthe scanning direction and columns in the direction transverse to thescanning direction. In the scanning direction, it is desirable thatdifferent sensor channels in the same row (e.g., all sensor channels inthe same row 204 of sensor array 202 of FIG. 2) sample the sameobject-space pixel (at somewhat different times) as the sensor arrayrotates. This can be achieved in part by coordinating sampling intervalswith the rotation of the sensor array, as described below. However, itis also important to avoid pointing error due to differences in thelocations of different sensor channels relative to the optical axis ofthe bulk optical module. Accordingly, in some embodiments, the bulkoptical module used with a sensor array in a scanning sensor system isdesigned to provide uniform sampling in both the scanning andnon-scanning directions.

FIGS. 24A and 24B are simplified conceptual illustrations showing thepotential for pointing error in a scanning system using a sensor array.FIG. 24A shows a row of a sensor array 2400 that has uniformly spacedsensor channels 2402 a-2402 d, which may correspond, e.g., to sensorchannels in a row 204 of sensor array 200 of FIG. 2. Each sensor channelhas a channel field of view through a bulk optic 2410, as indicated bydashed lines. Uniformly-spaced object space pixels, indicated by ovals2404 a-2404 d, align with the channel fields of view of sensor channels2402 a-2402 d. FIG. 24B shows sensor array 2400 after rotating throughan angle such that sensor channel 2402 a points approximately atobject-space pixel 2404 b. Sensor channel 2402 b points to the left ofobject-space pixel 2404 c, and sensor channel 2402 c pointsapproximately at object-space pixel 2404 d.

As can be seen in FIG. 24B, there is pointing error. For instance, thefield of view of sensor channel 2402 b does not point at object-spacepixel 2404 c, and the field of view of sensor channel 2402 c does notprecisely align with object-space pixel 2404 d. The term “intrapixelpointing error” is used herein to refer to differences in the field ofview between sensor channels that are nominally pointed at the sameobject-space pixel. (These differences are “intrapixel” with respect toobject-space pixels.) In some embodiments, controlling intrapixelpointing error is desirable when gathering multispectral pixel data.

In addition to intrapixel pointing error, a sensor system may have“interpixel pointing error,” which refers to nonuniform spacing betweenobject-space pixels in either the row (scanning) direction or the column(non-scanning) direction. In a scanning sensor system, uniformity ofpixel spacing in the scanning direction can be achieved by controllingthe shutter intervals relative to the rotation angle of the sensorsystem (e.g., as described below) and by limiting the intrapixelpointing error. In the non-scanning direction, it is desirable that theobject-space pixels along a column are uniformly spaced and that columnsin object space map to columns in image space. In this connection, itshould also be noted that some sensor arrays (e.g., sensor array 200)may include a set of staggered sensor channels (e.g., LIDAR channels202). In this case, a single column of object-space pixels can be imagedby scanning the array and controlling the shutter intervals to create acolumn alignment. For example, in the case of sensor array 200, a columnof the image can have sixteen pixels, even though the sixteen sensorchannels 202 are not aligned in a column on sensor array 200.

The desired imaging behavior is achieved in some embodiments byproviding a bulk optic module that has a focal length distortion profilein which displacement of a light ray is linear with changes in thetangent of the angle of incidence (θ) of the ray. Lenses (or lenssystems) with this type of focal length distortion profile are commonlyreferred to as “F tan θ” lenses (signifying that the displacementdistance at the image plane is a linear function of tan θ), or “flatfield” lenses. For small angles θ, an F tan θ lens has the property thatthe displacement of a light ray on the image plane (i.e., the sensorarray) is approximately linear with changes in the angle of incidence(θ) of the ray. In the scanning direction, this provides the desiredbehavior of reducing intrapixel pointing error. In the non-scanningdirection, this provides uniform sampling in object space for sensorrows spaced with a uniform pitch and also allows columns of object-spacepixels to map to columns of image-space pixels, even if the sensors arearranged in a staggered fashion.

FIG. 25 illustrates an example of an imaging system using an F tan θbulk optic module. Image plane 2502 includes a row of sensors 2504 a-gseparated by a uniform distance p (also referred to herein as the“linear pitch”). Sensors 2504 a-g can be, for example, a row (or aportion of a row) of sensor channels in any of the multispectral sensorarrays described above, or other sensors that detect photons from agiven direction. A bulk optic module 2506 is positioned at a distance fabove image plane 2502, where f is the focal length of bulk optic module2506. In this example, bulk optic module 2506 is represented as a singlebi-convex lens; however, it should be understood that other lenses ormulti-lens systems may be used.

Bulk optic module 2506 can be designed to focus light from a field ofview (or object space) onto image plane 2502. For instance, rays 2520a-2520 g indicate chief rays for sensors 2504 a-2504 g. (It should beunderstood that the actual path of light through bulk optic module 2506is not shown.)

Bulk optic module 2506 has a F tan θ focal-length distortion profile.(Those skilled in the art will understand how to create bulk opticmodules that have this profile, and a detailed explanation is omitted.)As a result, at least for small angles, a uniform change in the angle ofincidence of a light ray results in shifting the point where therefracted light ray intersects the image plane by a uniform distance,independently of the original angle of incidence. For instance, for rays2520 a, 2520 b, the difference in angle of incidence is α, and rays 2520a, 2520 b are separated at the image plane by the linear pitch p. Rays2520 b, 2520 c also have a difference in angle of incidence of α, andthe corresponding refracted rays 2520 b, 2520 c are also separated atthe image plane by the linear pitch p. Thus, if image plane 2502 andbulk optic module 2506 are together rotated through an angle α, ray 2520a originating from point 2530 a would become (approximately) the chiefray for sensor 2504 b while ray 2520 b originating from point 2530 bwould become (approximately) the chief ray for sensor 2504 c, and so on.The rotation angle α that corresponds to linear pitch p at the imageplane is referred to herein as the “angular pitch” of the scanningsystem, and the value of α is determined based on the sensor pitch p andthe properties of the bulk optic module. In scanning ranging/imagingsystems where the bulk optic module provides an angular pitch α suchthat scanning the system through the angle α results in shifting theincident rays by one linear pitch unit p, different sensor channels in arow can image the same portion of the field of view by acquiring imagesat a sequence of time steps, where the sensor array is rotated by theangular pitch α (or through a smaller angle such that a is an integermultiple of the scanning pitch) at each time step. Examples of scanningoperations of this type are described in more detail below.

Using an F tan θ lens can reduce intrapixel pointing error to anegligible level, where “negligible” can be quantified based on the sizeof the field of view of a sensor channel. FIG. 26 shows an example ofintrapixel pointing error that can be quantified and constrained in someembodiments of scanning systems. Circle 2602 represents the nominallocation of an object-space pixel; point 2604 is the center of circle2602. Circle 2612 (dashed line) represents the field of view sampled bya particular sensor channel when nominally pointed in the direction ofcircle 2602. As can be seen, center point 2614 of circle 2612 is offsetfrom the center 2604 of object-space pixel 2602 by an offset ε. Thisoffset can be used to quantify intrapixel pointing error. In someembodiments, intrapixel pointing error is considered negligible if theoffset ε for any given sensor channel in a sensor row is less than 50%of the diameter of the channel field of view. In other embodiments, atighter definition, e.g., that intrapixel pointing error is less than10% of the diameter of the channel field, of view is used. Whether agiven sensor system satisfies this constraint can be determined, e.g.,by imaging a test pattern. Other definitions can also be used.

The bulk optic for a scanning sensor system can also have an F tan θfocal-length distortion profile in the non-scanning direction. Thus, inthe example shown in FIG. 25, sensors 2504 a-g can also be understood ascorresponding to a column (or a portion of a column) of sensor channelsin any of the multispectral sensor arrays described above. Where some orall of the columns of sensor channels are staggered (e.g., LIDAR sensorchannels 202 in FIG. 2), a bulk optic having an F tan θ focal-lengthdistortion profile in both directions can allow the staggeredsensor-channel columns to sample a uniformly-spaced column ofobject-space pixels via a scanning operation and allow different sensorchannels in the same row to have negligible intrapixel pointing error.

It should be noted that an F tan θ bulk optical module can be useful incontexts other than multispectral sensor arrays. For instance, ascanning LIDAR sensor array may include an array of staggered LIDARchannels arranged in columns, which may be operated in ascanning/rotating mode to image a field of view. Examples of suchsystems are described, e.g., in U.S. patent application Ser. No.15/685,384, filed Aug. 24, 2017 (published as U.S. Patent ApplicationPublication No. 2018/0059222), the disclosure of which is incorporatedherein by reference in its entirety. An F tan θ bulk optical module canbe used to provide that object-space pixels imaged by sensor channelslocated in different columns in the staggered array align vertically(i.e., in the column direction in image space) with each other and/or toprovide uniform spacing of the sampled locations along the columns.

It should be understood that a bulk optic module for a sensor array(multispectral or LIDAR-only) is not required to have an F tan θfocal-length distortion profile, or any other particular focal-lengthdistortion profile. For instance, lenses used in some laser scanningsystems have a focal length distortion profile such that thedisplacement is a linear function of θ (rather than tan(θ)); such lensesare sometimes referred to as “F θ” lenses. For small angles of incidenceθ, tan(θ) is approximately equal to θ, and an F θ lens can provideapproximately the desired behavior. Accordingly, in some embodiments thebulk optic can have an F θ focal length distortion profile. Further, thefocal-length distortion profiles in the scanning and non-scanningdirections need not be the same.

In some embodiments, nonuniformity in the size or location of regionssampled by different sensors of a sensor array can be accounted forusing image-processing techniques. For instance, image processingalgorithms can interpret images with fisheye distortion or the like, aslong as the distortion profile of the bulk optic is not subject tolocalized deviations (e.g., high-frequency noise).

Alternatively, sensor channels can be arranged in a nonuniform arrayrather than a rectilinear array, in a pattern that compensates for thedistortion profile of the bulk optic so that uniform sampling of objectspace and consistent pointing behavior is achieved. For example, FIG. 27shows a nonuniform array pattern 2750 that compensates for barreldistortion. Sensor channels can be placed, e.g., at vertices 2752. (Somevertices 2752 are highlighted as red dots, but it should be understoodthat sensor channels can be placed at any vertex 2752). In this example,the spacing between adjacent sensor channels increases toward the centerof the array. FIG. 28 shows a nonuniform array pattern 2860 thatcompensates for pincushion distortion. Sensor channels can be placed,e.g., at vertices 2862. In this example, the spacing between adjacentsensor channels decreases toward the center of the array.

More generally, based on the design of a particular bulk optic, thedistortion profile in the image plane can be mapped, and sensor channelscan be placed non-uniformly such that sampling density is uniform inobject space. (It is noted that this technique may complicate design andmanufacture of sensor arrays and may require the sensor array to beadapted to a particular bulk optic.)

Further, in some embodiments, shutter intervals can be controlledindividually for different sensor channels, so that different sensorchannels can begin and end data collection for a given pixel atdifferent times. Individual shutter control can be used to compensatefor intrapixel pointing error of specific channels along the scanningdirection. (It is noted that this may complicate design of the sensorelectronics.)

2.5.3. Optics for Raster Scanning Systems

In some embodiments, multispectral sensor arrays of the kind describedabove may be used in a raster scanning mode. In a raster scanning mode,a sensor array having a relatively small number of sensor channels canscan the field of view in two directions to produce an image having anumber of pixels larger than the number of sensor channels. Forconvenience, the scanning directions are referred to herein as“horizontal” and “vertical”; however, those skilled in the art willunderstand that the spatial orientation of a raster scan is arbitrary.Raster scanning can be performed with a sensor array that includes a 2Darray of hybrid sensor channels (e.g., sensor array 600) ormultispectral pixels (e.g., sensor array 900), or with a row-basedscanning sensor array (e.g., sensor array 200) that also scans in acolumn-wise direction.

FIG. 29 shows an example of raster scanning using a sensor arrayaccording to an embodiment of the present invention. Sensor array 2900includes a number of sensor channels 2902 arranged in a regular sensorgrid. In this example, the sensor grid is 3×3; however, the dimensionscan be varied as desired. Sensor channels 2902 can include any of thesensor channel types described above. Arrow 2904 indicates a motion pathfor sensor array 2900. As indicated, sensor array 2900 can be moved tothe right along a horizontal line through a succession of imagingpositions within a field of view 2920, including positions 2912 and2914. At each imaging position, sensor channels 2902 can be operated tocapture an image. At the end of the horizontal line (position 2914),sensor array 2900 can be shifted down, e.g., by a pitch distance basedon the number of rows in sensor array 2900, to position 2916 to capturethe next image. Sensor array 2900 can then be moved to the left andcapture images for the next horizontal line. The captured images can beaccumulated into a larger image covering the entire field of view 2920.

Sensor array 2900 can be, e.g., any of the multispectral sensor arraysdescribed above. If sensor array 2900 is a 2D array (e.g., sensor array600 or sensor array 900), then the distance that sensor array 2900 movesbetween successive images along a horizontal scan line can be based onthe horizontal size of the array, to provide uniform, non-overlappingsamples as shown in FIG. 29. If sensor array 2900 is a row-based arrayand the rows are oriented along the horizontal scan lines, then thedistance between successive images along a horizontal scan line can beequal to the channel pitch, allowing different sensors in the same rowof the sensor array to image the same object-space pixel. The verticalshift between scan lines can be determined based on the number of rowsin the array.

The motion pattern of a raster scan can be varied from that shown inFIG. 29. For example, a “horizontal retrace” pattern can be used inwhich, at the end of a horizontal scan line, sensor array 2900 returnsto the left end and shifts down to the next horizontal scan line, sothat images for each horizontal scan line are captured using the samedirection of travel. As another example, for a row-based sensor array,the rows can be oriented in the vertical direction, and the verticaldistance between horizontal scan lines can be equal to the channel pitchwithin a row. (As noted above, “vertical” and “horizontal” arearbitrary.) Raster scanning can be implemented by physically moving thearray in two dimensions or by providing an optical system with atip-tilt mirror that can steer light in a raster pattern.

Some embodiments of a raster-scanning system can include sensor array2900 and a bulk optic module that supports uniform sampling of field ofview 2920. If the bulk optic module introduces a global distortion(e.g., barrel distortion or pincushion distortion), the resulting imageof field of view 2920 will not be uniformly sampled. By way ofillustration, FIG. 30 shows a nonuniform sampling pattern that canresult from raster scanning using a sensor array with a bulk optic thatexhibits pincushion distortion. Each grid 3001-3006 represents thelocations imaged with the sensor at a different location in the rasterpattern. As can be seen, the distortion is subject to local deviations.This type of localized distortion pattern can create significantdifficulty for subsequent image processing and analysis (much more sothan global pincushion distortion).

As described above, use of a bulk optical module with F tan θfocal-length distortion profile can provide uniform sampling across asensor array. Accordingly, an F tan θ bulk optical module can be used ina raster-scanning system. Alternatively, the sensor channels of a sensorarray for a raster-scanning system can be arranged to compensate for thedistortion profile of the bulk optical module, e.g., as described abovewith reference to FIGS. 27 and 28.

It should be understood that the foregoing examples of optical elementsand optical modules are illustrative and that variations andmodifications are possible. Further, optical elements shown inconnection with one type of sensor array can also be used with othertypes of sensor arrays. For instance, achromatic bulk optic modules canbe used in both row-based (or 1D) and 2D multispectral sensor arrays. Anachromatic bulk optic module can have an F tan θ focal length distortionprofile, an F θ focal length distortion profile, or a different profileas desired. Likewise, a bulk optic module with chromatic aberration canhave an F tan θ focal length distortion profile, an F θ focal lengthdistortion profile, or a different profile as desired. As noted above,achromatic bulk optics may be desirable for sensor arrays that includemultispectral sensor channels and/or hybrid sensor channels; however,this is not required.

3. Ranging/Imaging Systems with Multispectral Sensor Arrays

Multispectral sensor arrays of the kind described above can beincorporated into ranging/imaging systems that provide multispectralimages of a field of view (e.g., color images, absorption images,polarization images, and/or other images extracted from ambient-lightsensor channels) that are inherently registered with each other and withdepth information (e.g., extracted from LIDAR sensor channels in themultispectral sensor array). The particular implementation of amultispectral ranging/imaging system depends in part on the particularmultispectral sensor array. For purposes of illustration, two types ofranging/imaging systems will be described. A first type, referred toherein as an “angular scanning” (also sometimes called “rotating” or“spinning”) ranging/imaging system either rotates the sensor array (andits associated optics) to point at different portions of the field ofview at different times or uses controllable optics (e.g., MEMSgalvanometers) to direct light from different portions of the field ofview onto the array at different times. In either case, an angularscanning system allows different sensor channels on the same array(e.g., different sensors in a row of sensor array 200 of FIG. 2) toimage (detect photons from) a given area within the field of view atdifferent times. A second type, referred to herein as a “static” (or“solid-state”) ranging/imaging system, uses a 2D multispectral sensorarray that can image a field of view in multiple channels withoutmovement of the sensor array.

3.1. Angular Scanning Ranging/Imaging Systems

FIG. 31A shows an example of an automotive application for an angularscanning (e.g., rotating or spinning) imaging/LIDAR system 3100incorporating a sensor array as described herein. The automotiveapplication is chosen here merely for the sake of illustration and thesensors described herein may be employed in other types of vehicles,e.g., boats, aircraft, trains, etc., as well as in a variety of otherapplications where 3D depth images that are spatially and temporallyregistered with spectral images are useful, such as medical imaging,geodesy, geomatics, archaeology, geography, geology, geomorphology,seismology, forestry, atmospheric physics, laser guidance, airbornelaser swath mapping (ALSM), and laser altimetry. According to someembodiments, scanning imaging/LIDAR system 3100 can be mounted on theroof of a vehicle 3105 as shown. In other embodiments one or more LIDARand/or imaging sensors can be mounted on other locations of a vehicleincluding, but not limited to, the front or back of the vehicle, thesides of the vehicle and/or corners of the vehicle.

The scanning imaging/LIDAR system 3100 shown in FIG. 31A can incorporatea light source module 3102 for emitting laser pulses, such as transmitmodule 1510 of FIG. 15, and/or light sensing module 3104, such asreceiving module 1540 of FIG. 15, which can incorporate a sensor arraythat includes both LIDAR sensor channels and ambient-light sensorchannels (e.g., any of the multispectral sensor arrays described above).In some embodiments, light transmission module 3102 can be disposed inthe same housing as light sensing module 3104.

Scanning imaging/LIDAR system 3100 can employ a scanning architecture,where the orientation of the LIDAR light transmission module 3102 andlight-sensing module 3104 can be scanned around one or more fields ofview 3110 (e.g., a 360 degree field in some embodiments) within anexternal field or scene that is external to the vehicle 3105. In thecase of the scanning architecture, emitted light 3112 can be scannedover the surrounding environment as shown. For example, the outputbeam(s) of one or more light sources (such as infrared or near-infraredpulsed IR lasers, not shown) located in the scanning imaging/LIDARsystem 3100 can be scanned, e.g., rotated, to illuminate a scene aroundthe vehicle. In some embodiments, the scanning, represented by rotationarrow 3115, can be implemented by mechanical means, e.g., by mountingthe light emitters and sensors to a rotating column or platform. In someembodiments, the scanning can be implemented through other mechanicalmeans such as through the use of galvanometers. Chip-based steeringtechniques can also be employed, e.g., by using microchips that employone or more MEMS based reflectors, e.g., such as a digital micro-mirror(DMD) device, a digital light processing (DLP) device, and the like. Foremitters, such mirror subsystems can be controlled to direct light ontodifferent portions of the field of view at different times, and forsensors, such mirror subsystems can be controlled to direct light fromthe field of view onto different portions of the sensor array atdifferent times. In some embodiments, the scanning can be effectuatedthrough non-mechanical means, e.g., by using electronic signals to steerone or more optical phased arrays.

Objects within the scene (e.g., object 3110) can reflect portions of thelight pulses that are emitted from the LIDAR light sources. One or morereflected portions then travel back to the imaging/LIDAR system and canbe detected by the detector circuitry. For example, reflected portion3114 can be detected by light sensor module 3104. In addition, ambientlight 3116 may enter detector circuitry 3104.

FIG. 31B is a side view showing a simplified example of the structure ofscanning imaging/LIDAR system 3100 according to some embodiments.Scanning imaging/LIDAR system 3100 can include a stationary base 3120that can be mounted, e.g., to the roof of vehicle 3105. Rotationalhousing 3122, which holds emitter module (Tx) 3102 and light sensormodule (Rx) 3104 can be rotationally coupled to stationary base 3120.

FIG. 32 illustrates a block diagram of a rotating imaging/LIDAR system3200 (e.g., implementing scanning imaging/LIDAR system 3100 of FIG. 31)according to some embodiments. Rotating imaging/LIDAR system 3200 canoptionally employ a rotary actuator with wireless data and powertransmission and reception capabilities. In some embodiments, the rotaryactuator includes a rotor that is integrated onto a surface of arotating circuit board and a stator that is integrated onto a surface ofa stationary circuit board, and both board assemblies are equipped withwireless power and data transfer capabilities.

Rotating imaging/LIDAR system 3200 shown in FIG. 32 includes two mainmodules: a light ranging/imaging (R/I) device 3220 and a rotary actuator3215. Additionally, rotating imaging/LIDAR system 3200 can interact withone or more instantiations of user interface hardware and software 3205.The different instantiations of user interface hardware and software3205 can vary and may include, e.g., a computer system with a monitor,keyboard, mouse, CPU and memory; a touch-screen in an automobile; ahandheld device with a touch-screen; or any other appropriate userinterface. The user interface hardware and software 3205 may be local tothe object upon which rotating imaging/LIDAR system 3200 is mounted butcan also be a remotely operated system. For example, commands and datato/from rotating imaging/LIDAR system 3200 can be routed through acellular network (LTE, etc.), a personal area network (Bluetooth,Zigbee, etc.), a local area network (Wi-Fi, IR, etc.), or a wide areanetwork such as the Internet.

The user interface hardware and software 3205 can present the LIDAR datafrom the device to the user and/or allow a user or an upper levelprogram to control the rotating imaging/LIDAR system 3200 with one ormore commands. Example commands can include commands that activate ordeactivate the imaging/LIDAR system, specify photo-detector exposurelevel, bias, sampling duration and other operational parameters (e.g.,for emitted pulse patterns and signal processing), specify lightemitters parameters such as brightness. In addition, commands can allowthe user or an upper level program to select the method for displayingor interpreting results. The user interface can display imaging/LIDARsystem results which can include, e.g., a single frame snapshot image, aconstantly updated video image, and/or a display of other lightmeasurements for some or all pixels. Examples of other lightmeasurements for LIDAR pixels include ambient noise intensity, returnsignal intensity, calibrated target reflectivity, target classification(hard target, diffuse target, retroreflective target), range, signal tonoise ratio, target radial velocity, return signal temporal pulse width,and the like. In some embodiments, user interface hardware and software3205 can track distances (proximity) of objects from the vehicle and/oranalyze visual features determined from ambient-light sensor channels).Based on the visual features and distance information, user interfacehardware and software can, for example, identify and track objects inthe field of view and potentially provide alerts to a driver or providesuch tracking information for analytics of a driver's performance.

In some embodiments, the imaging/LIDAR system can communicate with avehicle control unit 3210, and one or more parameters associated withcontrol of a vehicle can be modified based on the received LIDAR and/orambient-light data. For example, in a fully autonomous vehicle, theimaging/LIDAR system can provide a real time 3D hyperspectral image ofthe environment surrounding the car to aid in navigation. In othercases, the imaging/LIDAR system can be employed as part of an advanceddriver-assistance system (ADAS) or as part of a safety system that, forexample, can provide 3D hyperspectral image data to any number ofdifferent systems (e.g., adaptive cruise control, automatic parking,driver drowsiness monitoring, blind spot monitoring, collision avoidancesystems, etc.). When a vehicle control unit 3210 is communicably coupledto light ranging/imaging device 3220, alerts can be provided to a driveror the proximity of an object can be tracked and/or displayed.

Light ranging/imaging device 3220 includes light sensing module 3230,light transmission module 3240, and light ranging/imaging systemcontroller 3250. Light sensor module 3230 can be similar to lightsensing module 1540 described above and can include a sensor array suchas sensor array 200 of FIG. 2 or sensor array 400 of FIG. 4. Lighttransmission module 3240 can be similar to light transmission module1510 described above. Rotary actuator 3215 includes at least two circuitboard assemblies, a lower circuit board assembly 3260 (also referred toherein as a base subsystem) and an upper circuit board assembly 3280(also referred to herein as a turret subsystem). The lower circuit boardassembly 3260 can be mechanically mounted to a fixed portion of anenclosure or housing (not shown) while the upper circuit board assembly3280 is free to rotate about an axis of rotation, usually defined by ashaft (not represented in FIG. 32) that is also mounted to the enclosure(directly or indirectly). The light ranging/imaging device 3220 can bemechanically attached to the rotatable upper circuit board assembly 3280and therefore is free to rotate within the housing.

While FIG. 32 shows one particular arrangement of components withinlight ranging/imaging device 3220 and rotary actuator 3215, in someembodiments, certain components may be integrated into one, or theother, module differently than shown. As one example, ranging/imagingsystem controller 3250, which can be, for example, an FPGA, ASIC, or amore general computing device, like an embedded system orsystem-on-a-chip (SOC), can be mounted directly (e.g., soldered) to, aprinted circuit board that is part of the upper circuit board assembly3280. In other words, in some embodiments, the parts of the rotaryactuator can be integrated within the light ranging/imaging device 3220and vice versa.

The rotary actuator 3215 includes a number of different systems that areintegrated onto one or more printed circuit boards of the lower andupper circuit board assemblies 3260 and 3280. For example, rotaryactuator 3215 can include a brushless electric motor assembly, anoptical communications subsystem, a wireless power transmissionsubsystem, and a base controller. These systems are formed by pairs ofcooperating circuit elements with each pair including one or morecircuit elements on the lower circuit board assembly 3260 operating incooperation with (e.g., having a function that is complementary to) oneor more circuit elements on the upper circuit board assembly 3280.Complementary functions include, for example, transmission (Tx) andreception (Rx) of power and/or data communication signals as isdescribed in more detail below.

The brushless electric motor assembly includes a stator assembly 3262integrated onto a printed circuit board of the lower circuit boardassembly 3260 and a rotor assembly 3282 integrated onto a printedcircuit board of the upper circuit board assembly 3280. The rotation ofrotor assembly 3282 is driven from a drive signal, for example, athree-phase drive current, that originates from a motor driver circuit3264. In some embodiments, one or more motor control lines connect themotor driver circuit to the coils of the stator assembly 3262 to allowfor the drive signal to be provided to the motor stator. Furthermore,the motor driver circuit 3264 can be electrically connected to a basecontroller 3266 such that the base controller 3266 can control therotation rate of the rotor assembly and thus the rotation rate (i.e.,frame rate) of the light ranging/imaging device 3220.

In some embodiments, rotor assembly 3282 can rotate at a rate between10-30 Hz. In some embodiments, the rotor assembly 3282 can be a passivedevice that includes a series of permanent magnets that are attached toa circuit board of the upper circuit board assembly. These permanentmagnets are either attracted to or repelled by an electromagnetic force,for example, a magnetic force, generated by the coils of the statorassembly to drive a rotation of the upper circuit board assembly 3280relative to the lower circuit board assembly 3260. The rotationalorientation of the upper circuit board assembly 3280 can be tracked by arotary encoder receiver 3294, which can track the angular position ofthe upper circuit board assembly by detecting the passage of one or morefeatures on the rotary encoder 3274. A variety of different rotaryencoder technologies can be employed. In some embodiments, rotaryencoder 3274 is integrated directly onto a surface of a circuit board ofthe lower circuit board assembly 3260.

Rotary actuator 3215 can also include a wireless power system thatincludes a wireless power transmitter 3272 and a wireless power receiver3292 in a configuration referred to herein as a rotary transformer.Power transmitted from transmitter 3272 to wireless power receiver 3292can be consumed by light ranging/imaging device 3220 and/or anycircuitry needing power on the turret/upper circuit board assembly. Insome embodiments, all power required by light ranging/imaging device3220 is provided through wireless power receiver 3292 and thus there isno need for a rotary electric coupler like a slip ring or mercury baseddevice thereby increasing reliability and decreasing cost of the overallsystem.

Rotary actuator 3210 can also include an optical communication subsystemthat includes a number of optical transmitters (e.g., opticaltransmitters 3278 and 3296) and a number of optical receivers (e.g.,optical receivers 3276 and 3298) used for bi-directional contactlessdata transmission between rotary actuator 3215 and light ranging/imagingdevice 3220 (or to/from any other device or system that is mechanicallyconnected to upper circuit board assembly 3280 of the rotary actuator3215). More specifically, the optical communication subsystem caninclude a set of base optical communication components that are attachedto (e.g., soldered to) lower circuit board assembly 3260 that is part ofthe stationary base of imaging/LIDAR system 3200, and can include a setof turret optical communication components that are attached to (e.g.,soldered to) rotating upper circuit board assembly 3280 that is part ofthe rotating turret of imaging/LIDAR system 3200. These opticalcommunication components provide an uplink data channel for providingoptical signals, including control signals, to light ranging/imagingdevice 3220 and also provide a downlink data channel for providingoptical signals, including ranging and operational data, from lightranging/imaging device 3220 to base controller 3266, user interfacehardware and software 3205, and/or the vehicle control unit 3210.

A downlink optical communication channel from the upper circuit boardassembly 3260 to the lower circuit board assembly 3280 can be createdbetween the optical downlink transmitter 3296 and the optical downlinkreceiver 3276. Light ranging/imaging device 3220 can be connecteddirectly to upper circuit board assembly 3280 and therefore can accessthe downlink optical communication channel to pass ranging andoperational data down to lower circuit board assembly 3260 for furtheruse. In some embodiments, the data passed down in the optical signalsvia the optical downlink can include range data for individual points(pixels) in the field (or possibly multiple ranges for a single pixeland angle, e.g. during fog/rain, when looking through glass windows,etc.), azimuth and zenith angle data, signal to noise ratio (SNR) of thereturn or signal intensity, target reflectivity, ambient near IR (NIR)levels coming from each pixel field of view, diagnostic operationalinformation from the light ranging/imaging device such as temperature,voltage levels, etc. In addition, data from any other system connectedto upper circuit board 3280 of the rotary actuator can be passed downthrough the optical downlink. For example, data from high speed RGB orthermal cameras, line scan cameras and the like.

An uplink optical communication channel from lower circuit boardassembly 3260 can be created between optical uplink transmitter 3278 andoptical uplink receiver 3298. In some embodiments, control signals fromthe base controller 3266 can be passed to light ranging/imaging device3220 via the optical uplink communication channel. For example, in someembodiments, base controller 3266 can monitor various temperatures inthe device (as received from the downlink channel) and can, in the caseof an overheat condition, send an emergency shutdown signal to lightranging/imaging device 3220 via the uplink channel. In some embodiments,the base controller can be a mobile computer, e.g., a programmablesystem-on-a-chip employing an ARM+FPGA architecture with associatedmemory and I/O capability (e.g., Ethernet and the like).

Ranging data can be generated by light ranging/imaging device 3220 bytransmitting one or more light pulses from light transmission module3240 to objects in a field of view surrounding the light ranging/imagingdevice. Reflected portions of the transmitted light are then detected bylight sensing module 3230 after some delay time. Based on the delaytime, commonly referred to as the “time of flight”, the distance to thereflecting surface can be determined. Other ranging methods can beemployed as well, for example, continuous wave, Doppler, and the like.

In addition to ranging data, light ranging/imaging device 3220 cangenerate light intensity data based on ambient light. For instance,light sensing module 3230 can include one or more ambient-light sensorchannels tuned to various wavelength bands (e.g., as described above),and the ambient-light sensor channels can be operated to count photonsof the channel wavelength band detected during a particular timeinterval (referred to herein as a “shutter interval”). The photon countsin a particular channel are indicative of intensity of light in thatwavelength band. Other ambient light sensor channels can be used tomeasure other characteristics of the ambient light, such as polarization(e.g., by determining the difference in photon counts detected bydifferently-oriented polarization channels) and/or absorption at aparticular wavelength (e.g., by comparing the number of photons in achannel tuned to the absorption band relative to number of photons inanother channel tuned to a wider band that includes the absorption band,with a deficit in the absorption band indicating absorption).

Light transmission module 3240 can include an emitter array 3242 (e.g.,emitter array 1520 described above) and a Transmit (Tx) optical system3244 (including, e.g., Tx optical modules described above). Lighttransmission module 3240 can further include a processor 3246 and memory3248, although in some embodiments these computing resources can beincorporated into ranging/imaging system controller 3250. In someembodiments, a pulse coding technique can be used, e.g., Barker codesand the like. In such cases, memory 3248 can store pulse-codes thatindicate when light should be transmitted. In one embodiment thepulse-codes are stored as a sequence of integers stored in memory.

Light sensing module 3230 can include a sensor array 3232 and a receiver(Rx) optical system 3234. Sensor array 3232 can be, e.g., animplementation of sensor array 200 or sensor array 400 (or similarsensor array) and can include rows of sensor channels that incorporateboth LIDAR sensor channels (or other ranging sensor channels) andambient-light sensor channels as described above.

As mentioned above, processor 3236 and memory 3238 (e.g., SRAM) canperform the signal processing. As an example of signal processing for aranging sensor channel, for each photosensor or grouping ofphotosensors, memory 3238 of light sensing module 3230 can accumulatecounts of detected photons over successive time bins and these time binstaken together can be used to recreate a time series of the reflectedlight pulse (i.e., a count of photons vs. time). This time-series ofaggregated photon counts is referred to herein as an intensity histogram(or just histogram). In addition, processor 3236 can apply certainsignal processing techniques, such as matched filtering, to help recovera photon time series that is less susceptible to pulse shape distortionthat can occur due to SPAD saturation and quenching. As an example ofsignal processing for an ambient-light sensor channel, for eachphotosensor or grouping of photosensors, memory 3238 of light sensingmodule 3230 can accumulate counts of detected photons over a single timeinterval (referred to herein as a “shutter interval”). The shutterinterval can be, e.g., as long as the aggregate length of the time binsused to construct the intensity histogram for the ranging sensorchannels, or it can be a longer or shorter time interval. The photoncount accumulated by a particular ambient-light sensor channel during ashutter interval can indicate the intensity of light received by thatambient-light sensor channel. In some embodiments, processor 3236 canapply signal processing techniques, e.g., calibration-based correctionsto reduce noise and/or to compensate for channel-to-channel variation inintensity measurements. In some embodiments, one or more components ofranging/imaging system controller 3250 can also be integrated into thesame ASIC as sensor array 3232, processor 3236 and memory 3238, therebyeliminating the need for separate a ranging controller module.

In some embodiments, output from processor 3236 is sent toranging/imaging system controller 3250 for further processing. Forexample, the data can be encoded by one or more encoders ofranging/imaging system controller 3250 and then sent as data packets viathe optical downlink to lower circuit board assembly 3260.Ranging/imaging system controller 3250 can be realized in multiple waysincluding, e.g., by using a programmable logic device such an FPGA, asan ASIC or part of an ASIC, using a processor 3252 with a memory 3254,and some combination of the above. Ranging/imaging system controller3250 can cooperate with base controller 3266 or operate independently ofthe base controller (via pre-programed instructions) to control lightsensing module 3230 by sending commands that include start and stoplight detection and adjust photo-detector parameters. Similarly,ranging/imaging system controller 3250 can control the lighttransmission module 3240 by sending commands, or relaying commands fromthe base controller 3266, that include start and stop light emissioncontrols and controls that can adjust other light-emitter parameterssuch as, emitter temperature control (for wavelength tuning), emitterdrive power and/or voltage.

If emitter array 3242 has multiple independent drive circuits, thenthere can be multiple on/off signals that can be properly sequenced byranging/imaging system controller 3250. Likewise, if the emitter arrayincludes multiple temperature control circuits to tune differentemitters in the array differently, the transmitter parameters caninclude multiple temperature control signals. In some embodiments,ranging/imaging system controller 3250 has one or more wired interfacesor connectors (e.g., traces on a circuit board) for exchanging data withlight sensing module 3230 and with light transmission module 3240. Inother embodiments, ranging/imaging system controller 3220 communicateswith the light sensing module 3230 and light transmission module 1840over a wireless interconnect such as an optical communication link.

While a particular example of a scanning ranging/imaging system has beendescribed in detail, those skilled in the art with access to the presentdisclosure will recognize that other implementations are possible,including scanning ranging/imaging systems that perform raster scanningin two dimensions. Raster scanning mechanisms may include, e.g.,electric motors to move the sensor array in two dimensions (e.g., rotarymovement around one axis combined with linear or rotary movement alongor around an orthogonal axis), tip-tilt mirror systems that arerotatable around two or more orthogonal axes, or a combination of motionof the sensor array and a mirror system (e.g., the raster scanningmechanism may move the sensor array in one direction and move mirrors toprovide scanning in an orthogonal direction).

3.2. Operation of Scanning Ranging/Imaging Systems

In an example of an imaging operation, the rotation (or other scanning)of light ranging/imaging device 3220 can be coordinated with the shutterintervals (which may correspond to LIDAR active-sensing intervals) suchthat a given location within the field of view is successively imaged byeach sensor channel in a row of the sensor array. That is, the timebetween shutter intervals can be based on the angular distance betweenadjacent image pixels divided by the rotation rate of the imaging/LIDARsensor array. Since the sensor channels image the same point in space(at slightly different times), registration between images obtained fromdifferent channels is inherent, with no need for object-identificationor point-mapping algorithms. Further, if the speed of the imagingoperation is sufficiently fast, it can be assumed that little change hasoccurred between imaging with successive channels, so the imagescorrespond to the same scene. Thus, in some embodiments, a row-basedsensor array such as sensor array 200 or sensor array 400 can enablemultispectral imaging across a wide field of view (e.g., up to 360degrees).

FIGS. 33A and 33B illustrate an example of multispectral imaging withinherent registration between imaging channels using an imaging/LIDARsensor array similar to sensor array 200 or sensor array 400 describedabove. FIG. 33A shows a field of view 3300 to be scanned (e.g., a360-degree field). For purposes of illustration, the description of theimaging process will refer to a specific image region 3302 within fieldof view 3300; however, the same principles can apply to all portions offield of view 3300.

FIG. 33B shows the progress of data collection at successive stages in ascanning operation that uses a row-based imaging/LIDAR sensor array(e.g., any of sensor array 200, 400, or 500) to create a set ofinherently registered images of region 3302. In this example, the sensorarray (not explicitly shown) is assumed to have five ambient-lightchannels tuned to different colors (or wavelength regions) and one LIDARchannel in each sensor row. It is also assumed that the ambient-lightsensor channels within a row of the sensor array are spaced apart by auniform linear pitch p and that the bulk optic module provided for theimaging/LIDAR sensor array has a F tan θ focal-length distortion profileso that rotation of the imaging/LIDAR system through pitch angle αshifts the field of view approximately by the linear pitch p (e.g., asdescribed above).

At a first time (t=1), the sensor array is operated for a first shutterinterval. Each channel collects data corresponding to a differentlocation (or object-space pixel) in region 3302, as indicated byrepresentative colored dots 3305. For instance, the object-space pixelindicated by box 3309 is sampled (or imaged) by a green sensor channel3306G. It is to be understood that the actual number of sensor channelscan be significantly larger than the number of colored dots 3305 shownin FIG. 33B; for instance, there may be more than five rows of sensors,and the density of rows may be significantly higher than what is shown.

At time t=2, the sensor array has moved through the pitch angle α,which, relative to region 3302, shifts each channel to the right by adistance equal to the liner pitch p; colored dots 3305 have shifted onepitch to the right. At this time, the sensor array is operated for asecond shutter interval, in which object-space pixel 3309 is sampled bya yellow sensor channel 3306Y. (For times t=2 and later, the white dots3307 indicate locations that were sampled by at least one sensor channelcorresponding to a colored dot 3305 in a previous shutter interval butthat are not currently being sampled by a channel corresponding to anyof colored dots 3305.)

At time t=3, the sensor array has again moves through the same pitchangle α, shifting each channel to the right by another pitch so that attime t=3, object-space pixel 3309 is sampled by an orange sensor channel33060. Similarly, at time t=4, object-space pixel 3309 is sampled by ared sensor channel 3306R. Proceeding in this manner, object-space pixel3309 (and other locations in region 3302) can eventually be sampled byevery sensor channel that is present in a particular row of the sensorarray, including LIDAR sensor channel 3312. It should be understood thatthe channel pitch may be small and the number of sampling intervals per360-degree rotation can be large (e.g., 1024, 2048, or 4096 samplingintervals per rotation), providing a higher image resolution than issuggested by FIG. 33B. The size and shape of object-space pixels isdetermined in the non-scanning direction by the spacing of the rows ofthe sensor array (and the size of the field of view) and in the scanningdirection by the angle between successive sampling operations. Dependingon the particular system design, object-space pixels can have a simpleaspect ratio (e.g., 1:1 or 2:1 or the like), which can facilitate imageprocessing and image analysis.

In this example, adjacent ambient-light sensor channels within a rowhave a uniform pitch p that facilitates inherent registration of imagescaptured using different sensors. As shown, LIDAR sensor channel 3302has a larger spacing than the uniform pitch of the ambient-light sensorchannels. In some embodiments, the spacing between LIDAR sensor channel3312 and the adjacent ambient-light sensor in a row can be an integermultiple of the uniform pitch p of the ambient-light sensor channels (inthe example, the top row of sensors has LIDAR sensor channel 3312 spacedby 2p from the closest ambient-light sensor channel), which still allowsinherent registration between the LIDAR sensor channel and theambient-light sensor channels. (This is shown in FIG. 33B.) Moregenerally, data from different sensor channels in a row can beinherently registered to the same location in the field of view,provided that the angular pitch of the sensor channels is an integermultiple of the angular displacement (or measurement angle) betweensuccessive shutter intervals, which is the case where the bulk opticmodule provided for the imaging/LIDAR sensor array has a F tan θfocal-length distortion profile. In embodiments where this condition isnot satisfied, imaging operations can be performed, and data fromdifferent sensor channels can be used to generate reliably registeredimages (since the spatial relationship between different sensor channelsis fixed); however, the image processing may become more complex.

In some embodiments, a rotating ranging/imaging system can rotatecontinuously (e.g., at a rate of 10-30 Hz) and can determine, based onthe current rotational angle when to start and stop data collection. Forexample, as described above with reference to FIG. 32, rotary actuator3215 can include rotary encoder 3274, and rotary encoder receiver 3294can track the angular position of upper circuit board assembly 3280(which is rigidly connected to the sensor array 3232). A set of M“measurement angles” ϕ_(i) (for i=1, 2, . . . M) corresponding touniformly spaced angular positions can be defined such thatϕ_(i)−ϕ_(i-1)=α/N for integer N (where α is the pitch angle of thesensor array). In some embodiments, N=1. The number M of measurementangles can be selected as M=360°/(α/N) (or more generally Θ/(α/N), whereΘ is the angle through which the sensor array moves during a scan). Inone example, rotary encoder 3274 has 2048 steps, and the sensor arrayand bulk optical module are designed such that α=360°/2048.

Sensor array 3232 can rotate (with the rest of light ranging/imagingdevice 3220) continuously at a uniform angular speed, and LIDAR sensorchannels can continuously generate signals. Memory 3238 can accumulatecounts of detected photons over successive time bins, which can be usedto create an intensity histogram as described above. A controller (e.g.,R/I system controller 3250 of FIG. 32) can receive a signal indicatingwhen the encoder position corresponds to one of the measurement anglesϕ_(i). This signal, also referred to as a “marker” signal, marks aboundary between consecutive measurement periods for the LIDAR sensorchannels. In response to this signal, histogram data collected in memory3238 can be sent to a digital signal processor (DSP) (e.g., processor3236) for analysis, which can include, e.g., applying filters to thehistogram data to determine the precise time of receipt of reflectedLIDAR pulses. In response to the same signal, memory 3238 can beginaccumulating data for the next histogram. In some embodiments, memory3238 can include two (or more) banks dedicated to storing photon-counts,and photon-count data from alternate measurement periods can be storedin alternate banks.

In some embodiments, the marker signal can also be used as a trigger toinitiate a shutter interval of the ambient-light sensor channels. Duringthe shutter interval, a single photon count (accumulated across theshutter interval) can be determined from signals received at eachambient-light sensor channel. The photon count from each ambient-lightsensor channel can be sent to the DSP along with the histogram data fromthe LIDAR sensor channels. The shutter interval can have the sameduration as a measurement period or a different (e.g., shorter) durationas desired. In some embodiments, the shutter interval may be dynamicallyvariable, e.g., based on current light levels in one or more of theambient-light sensor channels, with shorter shutter intervals beingselected to avoid saturating the photosensors and longer shutterintervals being selected under low-light conditions.

Continuous rotation during measurement can be used with multispectralsensor arrays as described above. Continuous rotation during measurementcan also be used with other types of sensor arrays, such as a LIDAR-onlysensor array that includes multiple columns of LIDAR channels (which maybe staggered, e.g., as shown in FIG. 1, and/or tuned to differentemission frequencies). It should also be understood that continuousrotation is not required. In some embodiments, a rotatingranging/imaging system can rotate and collect data in a stepwisefashion, e.g., rotating to a first measurement angle, collecting datafor a measurement period, then rotating to the next measurement angleand repeating the data collection.

3.3. Scanning with Increased Resolution in Ambient-Light Channels

In the example of FIGS. 33A-33B, a scanning ranging/imaging system usinga multispectral sensor array produces images with the same spatialresolution for all channel types. For some applications, it may bedesirable to increase the spatial resolution of ambient-light sensorchannels relative to the number of LIDAR channels. Examples ofmultispectral sensor arrays that can provide enhanced (increased)spatial resolution for ambient-light sensor channels in both thescanning and non-scanning directions will now be described.

FIG. 34 shows a simplified front view of a sensor array 3400 accordingto some embodiments. Sensor array 3400 can be a 1D sensor array similarto sensor array 200 of FIG. 2 described above, with LIDAR sensorchannels 202, each of which is associated with a row 3404 that includesambient-light sensor channels 3406 a-d. In this example, ambient-lightsensor channels 3406 a-d each have the same type of optical filter,which can be for example a broad-spectrum visible light filter (e.g.,having a passband from about 425 nm to about 700 nm). Various types ofoptical filters can be used (e.g., polarization filters, color filters,etc.), and in some embodiments ambient-light sensor channels 3406 a-dmay have no optical filter, in which case the range of wavelengthsdetectable by ambient-light sensor channels 3406 a-d is determined bythe wavelength range of the photosensors in ambient-light sensorchannels 3406 a-d. Ambient-light sensor channels 3406 a-d have different“subpixel” apertures (indicated by darkened squares 3410). It is to beunderstood that darkened squares 3410 indicate an opening in an apertureplane and that the aperture plane is opaque over other portions of thearea associated with channels 3406 a-d. In this example, each subpixelaperture exposes a different quadrant of the channel area.

In operation, sensor array 3400 can perform scanning as described abovewith reference to FIGS. 33A and 33B. As ambient-light sensor channels3406 a-d are scanned across an object-space pixel, each channel 3406 a-dsamples a different “subpixel” (i.e., a subset of the total area of theobject-space pixel) using the same type of optical filter. In thismanner, an ambient-light image with resolution four times the resolutionof LIDAR channels 202 can be generated. Accordingly, ambient-lightsensor channels such as channels 3406 a-d are also referred to as“enhanced-resolution” ambient-light sensor channels.

In the example of FIG. 34, each ambient-light sensor channel 3406 areceives a quarter of the incident light. In other embodiments, aspatial encoding scheme can be used to allow more light in while stillproviding data with subpixel resolution. For instance, FIG. 35 shows aset of four ambient-light sensor channels 3506 a-d withspatially-encoded subpixel apertures according to some embodiments. Inthis example, the aperture of channel 3506 a (darkened area) exposes thefull channel area, while the apertures of channels 3506 b, 3506 c, and3506 d each occlude (white area) a different quadrant of the channelarea. Intensity measurements (e.g., photon counts) C0-C3 from channels3506 a-d can be provided to an arithmetic logic circuit 3520, which canimplement the following equations to compute subpixel values for thesubpixels (S0, S1, S2, S3) of a pixel 3524:S1=C0−C3  (2a)S2=C0−C2  (2b)S3=C0−C1  (2c)S0=C0−(C1+C2+C3)=C1+C2+C3−2C0  (2d)

The examples of FIGS. 34 and 35 show subpixels as quadrants of a channelarea, which doubles the image resolution in each direction. Otherembodiments can provide different increases in resolution. For instance,higher resolution can be achieved by providing more ambient-lightchannels 3406 or 3506 with smaller (relative to the channel area)subpixel apertures; the upper limit on resolution may be based on theaperture size needed to measure intensity with acceptable accuracy. Insome embodiments, the subpixel apertures are arranged so that thesubpixels form a square grid (e.g., as shown in FIGS. 34 and 35), butthis is not required, and other sampling patterns (including rectangularrather than square patterns) may be used. Further, while the aperturesshown in FIGS. 34 and 35 are either squares or six-sided regions (withsquare indentations at one corner), this is also not required; circularapertures or apertures having other shapes may also be used. It isassumed that all ambient-light sensor channels in a group ofambient-light sensor channels that is used for subpixel sampling havethe same type of optical filter so that the same spectral information issampled at each information and the effect is to increase spatialresolution of the sampling. The particular filter type can be selectedas desired, including broad-spectrum filters, narrower bandpass filters,or any other type of optical filter.

In the examples of FIGS. 34 and 35, spatial resolution is increased inboth the scanning and non-scanning directions by using subpixelapertures. This approach (with or without spatial encoding) involvesusing one ambient-light sensor channel per subpixel, e.g., using fourambient-light sensor channels to provide a 4× enhancement in spatialresolution, or sixteen ambient-light sensor channels to provide a 16×enhancement. In other embodiments, sampling resolution in the scanningdirection can be increased by using temporal subdivision while samplingresolution in the non-scanning direction can be increased by usingsubpixel apertures. This can allow, for example, four ambient-lightsensor channels to provide a 16× enhancement in spatial resolution.

In some embodiments, temporal subdivision can be provided by usingmultiple integration registers to accumulate intensity data (e.g.,photon counts) for each ambient-light sensor channel, with differentintegration registers being active during different portions of ashutter interval (shutter intervals are described above with referenceto FIG. 33B). Assuming that the sensor array is continuously rotatingduring the shutter interval, this has the effect of measuring intensityseparately for different portions along the scanning direction (referredto for convenience as “column areas”) of the area occupied by anobject-space pixel.

FIG. 36 shows a simplified schematic diagram of a readout data path withmultiple integration registers 3602, according to some embodiments. Inthis example, it is assumed that a photosensor 3604 for a particularambient-light sensor channel provide data (e.g., a photon count) foreach time bin (as described above with reference to FIG. 32), where thetime bin is shorter than the shutter interval. The photon count for eachtime bin is delivered to a selected integration register 3602 in a bankof integration registers 3610, and the selected integration register3602 adds the photon count received from photosensor 3604 to its currentstored value. A selection signal is provided by bank selection logic3606 to select one of integration registers 3602.

In the example shown, the integration registers operate as follows: ateach clock cycle, a multiplexer 3620 is controlled by selection logic3606 to read out a stored value from a currently selected one ofintegration registers 3602. The current value 3622 thus selected isdelivered to an arithmetic logic unit (ALU) 3624, which also receives anew photon count from photosensor 3604. ALU 3624 adds the new photoncount to current value 3622 and delivers the result to integrationregister bank 3610. Selection logic 3606 selects the current one ofintegration registers 3602 to receive the new value. Otherimplementations can also be used.

In some embodiments of a scanning ranging/imaging system (e.g., system3200 described above) with a number (N) of integration registers,selection logic 3606 divides the shutter interval into a number N ofsub-intervals (where each sub-interval includes one or more clockcycles) and selects a different one of integration registers 3602 foreach sub-interval, so that each integration register 3602 accumulates apixel count for a different temporal portion (1/N) of the sub-interval.For instance, selection logic 3606 can use rotary encoder 3274 (as shownin FIG. 32) to define the sub-intervals, or sub-intervals may be definedbased on a timer used as a proxy for position based on a known speed ofscanning. At the end of the shutter interval, each integration register3602 can be read out to provide N intensity measurements per pixel.

Temporally subdividing each shutter interval in this manner can increasethe sampling resolution in the scanning direction. FIG. 37 illustratesambient light measurement using multiple integration registers for avehicle 3703, according to some embodiments. In this example, a scanningranging/imaging system 3701 (which may be, e.g., an implementation ofsystem 3200 described above) may be mounted on top of vehicle 3703.Scanning ranging/imaging system 3701 may be configured to rotate aroundits central axis many times per second (e.g., at 30 Hz) to scan thesurrounding area and generate a multispectral image as described abovewith reference to FIG. 33B.

In embodiments where a scanning ranging/imaging system provides temporalsubdivision for ambient-light sensor channels, the spatial resolution ofthe ambient light image in the scanning direction can be increased basedon the number of integration registers. In the example of FIG. 37, anintegration-register bank 3710 (which can operate similarly tointegration-register bank 3610 described above) includes fourintegration registers 3712 a-d. An increment of angular rotation 3702corresponding to a shutter interval can be subdivided into four angularincrements, during each of which received photon counts are accumulatedin a corresponding one of integration registers 3712 a-d (as indicatedby arrows 3716 a, 3716 b). This increases the spatial resolution of theambient-light image by a factor of four in the scanning direction.

It may also be desirable to increase the spatial resolution of theambient-light image in the non-scanning direction. In some embodiments,multiple ambient-light sensor channels with spatially-encoded subpixelapertures can be used for this purpose. FIG. 38A shows a set of fourambient-light sensor channels 3806 a-d that provide spatially-encodedsubpixel apertures according to some embodiments. Ambient-light sensorchannels 3806 a-d can be used to increase resolution by a factor of fourin both the scanning and non-scanning directions. In this example, theaperture (hatched-area) of ambient-light sensor channel 3806 a exposesone-quarter of the total channel area, while the apertures ofambient-light sensor channels 3806 b-d each expose 3/16 of the totalchannel area. Intensity measurements (e.g., photon counts) C0-C3 fromchannels 3806 a-3806 d can be provided to an arithmetic logic circuit3820, which can implement the following equations to compute subpixelvalues for four subpixels (S0, S1, S2, S3) of a pixel 3824:S0=C0−C2  (3a)S2=C0−C3  (3b)S3=C0−C1  (3c)S1=C0−(S1+S2+S3)=C2+C3+C1−2C0  (3d)As shown for pixel 3824, the four subpixels S0, S1, S2, S3 correspond tofour pixels occupying different rows in a column area that isone-quarter of the width (in the scanning direction) of the total areaof pixel 3824.

To fully populate subpixels in all column areas of the pixel, temporalsubdivision as illustrated in FIG. 37 can be used to enable a singleambient-light sensor channel to sequentially sample different columnareas during a shutter interval. FIG. 38B shows the effect of temporalsubdivision for ambient-light sensor channel 3806 a of FIG. 38Aaccording to some embodiments. In this example the shutter interval isdivided into four sub-intervals as described above with reference toFIG. 37. It is assumed that the shutter interval lasts from t=0 to t=1.During a first sub-interval (beginning at t=0), the aperture ofambient-light channel 3806 a is exposed to column area 3832 a of theobject-space pixel 3824, and intensity C00 for column area 3832 a ismeasured. During a second sub-interval (beginning at t=0.25), theaperture of ambient-light channel 3806 a is exposed to column area 3832b of object-space pixel 3824, and intensity C01 for column area 3832 bis measured. During a third sub-interval (beginning at t=0.5), theaperture of ambient-light channel 3806 a is exposed to column area 3832c of object-space pixel 3824, and intensity C02 for column area 3832 cis measured. During a fourth sub-interval (beginning at t=0.75), theaperture of ambient-light sensor channel 3806 a is exposed to columnarea 3832 d of object-space pixel 3824, and intensity C03 for columnarea 3832 d is measured. Thus, using temporal subdivision of a shutterinterval, ambient-light sensor channel 3806 a can successively sampleeach column area of object-space pixel 3824, providing four intensityvalues. As described above with reference to FIG. 33B, ambient-lightsensor channel 3806 b can traverse object-space pixel 3824 in the samemanner as shown in FIG. 38B, with an offset of one shutter interval (orsome other integer number of shutter intervals) to produce fourintensity values, and likewise for ambient-light sensor channels 3806 cand 3806 d. Applying the computational logic of FIG. 38A and Eqs.(3a)-(3d) separately to the four intensity values of each column areaprovides a total of sixteen subpixel samples using four ambient-lightsensor channels. Thus, a combination of spatial and temporal subdivisionof object-space pixels can provide an ambient-light image with enhancedresolution in both scanning and non-scanning directions. While theexample shown here increases resolution by a factor of four in eachdirection, other embodiments may provide greater or lesser enhancementas desired.

It will be appreciated that the examples of spatial and temporalsubdivision described herein are illustrative. The particular number,shapes, and sizes of apertures assigned to particular ambient-lightsensor channels can be varied, and any enhancement factor can beachieved (subject to physical constraints such as photosensor size andthe minimum size of an aperture that can be fabricated). Thus, spatialresolution in the scanning and/or non-scanning directions can beenhanced to a desired degree, and enhancement in the scanning andnon-scanning directions need not be equal. Enhancement of spatialresolution as described herein can be applied for any type ofambient-light sensor channel, regardless of what optical filters areused.

3.4. Static Ranging/Imaging Systems

Rotating ranging/imaging systems as described above can be implementedusing multispectral sensor arrays such as sensor array 200, sensor array400, or sensor array 500, where sensor channels of different types arearranged along a row that is scanned across the field of view. Otherexamples of sensor arrays described above (e.g., sensor array 600,sensor array 900) provide 2D arrays of identical multispectral and/orhybrid sensor channels (or pixels). While such arrays can be used in arotating system, rotation or other scanning motion is not required for a2D array of multispectral or hybrid pixels to image a two-dimensionalfield of view. Accordingly, some embodiments provide static (or“solid-state”) ranging/imaging systems in which the sensor array doesnot move in order to perform an imaging operation. It is to beunderstood that static ranging/imaging system may be mobile. Forinstance, one or more static ranging/imaging systems may be mounted on avehicle.

FIG. 39 is a side view showing a simplified example of the structure ofa static imaging/LIDAR system 3900 according to some embodiments.Imaging/LIDAR system 3900, which is an example of a staticranging/imaging system, can include a housing 3922, which holds emittermodule (Tx) 3902 and light sensor module (Rx) 3904. Housing 3922 can bemounted on a vehicle or in any other location where a ranging/imagingsensor is desirable.

FIGS. 40 and 41 are simple illustrations of exemplary implementations ofvehicle-mounted static electronic ranging/imaging systems according tovarious embodiments. Specifically, FIG. 40 illustrates an implementation4000 where static ranging/imaging systems 4002 a-d are implemented atthe outer regions of a road vehicle 4005, such as an automobile; andFIG. 41 illustrates an implementation 4100 where static ranging/imagingsystems 4102 a-b are implemented on top of a road vehicle 4105. In eachimplementation, the number of LIDAR systems, the placement of the LIDARsystems, and the fields of view of each LIDAR system can be chosen toobtain a majority of, if not the entirety of, a 360 degree field of viewof the environment surrounding the vehicle. Automotive implementationsfor the LIDAR systems are chosen herein merely for the sake ofillustration and the sensors described herein may be employed in othertypes of vehicles, e.g., boats, aircraft, trains, etc., as well as in avariety of other applications where 3D depth images are useful, such asany of the applications mentioned above with reference to FIG. 32. Itshould also be understood that static and rotating ranging/imagingsystems can be used together and that some ranging/imaging systems maybe configured for selectable operation in static or rotating mode.

With reference to FIG. 40, static ranging/imaging systems 4002 a-d canbe mounted at the outer regions of a vehicle, near the front and backfenders. Static ranging/imaging systems 4002 a-d can each be positionedat a respective corner of vehicle 4005 so that they are positioned nearthe outermost corners of vehicle 4005. That way, static ranging/imagingsystems 4002 a-d can better measure the distance of vehicle 4005 fromobjects in the field at areas 4006 a-d. Each static ranging/imagingsystem can face a different direction (possibly with partially and/ornon-overlapping fields of views between units) so as to capture acomposite field of view that is larger than each unit is capable ofcapturing on its own. Objects within the scene can reflect portions oflight pulses 4010 that are emitted from LIDAR Tx module 4008. One ormore reflected portions 4012 of light pulses 4010 then travel back tostatic ranging/imaging system 4002 a and can be received by Rx module4009, which can be disposed in the same housing as Tx module 4008. Rxmodule 4009 can include a multispectral sensor array (e.g., as describedabove) that receives ambient light as well as reflected light from LIDARTx module 4008.

In some embodiments, each of static ranging/imaging systems 4002 a-d canimage its entire field of view (shown as areas 4006 a-d, respectively)at one time. In other embodiments, static ranging/imaging systems 4002a-d can electronically scan a scene to capture images of the scene. Asused herein, “electronic scanning” refers to collecting data fordifferent portions of a scene at different times without physicalmovement (e.g., reorientation) of the sensor array; electronic scanningis thus distinguished from the rotating/spinning operations describedabove. Electronic scanning can be implemented, e.g., by activatingdifferent portions of a LIDAR emitter array and corresponding subsets ofthe LIDAR sensor channels at different times, or by other means, such aschip-based beam steering techniques, e.g., by using microchips thatemploy one or more MEMS based reflectors, such as a digital micromirror(DMD) device, a digital light processing (DLP) device, or the like tosteer light from Tx module 4008 such that it reflects onto differentportions of the sensor array at different times. Thus, staticranging/imaging system 4002 a can electronically scan between points4020 and 4022 to capture objects in the field at area 4006 a, andlikewise for systems 4002 b-d and areas 4006 b-d.

Although FIG. 40 illustrates four static ranging/imaging systems mountedat the four corners of a vehicle, embodiments are not limited to suchconfigurations. Other embodiments can have fewer or more staticranging/imaging systems mounted on other regions of a vehicle. Forinstance, static ranging/imaging systems can be mounted on a roof of avehicle, as shown in FIG. 41. In such embodiments, staticranging/imaging systems 4102 a-b can have a higher vantage point tobetter observe areas 4107 a-b around vehicle 4105.

As mentioned, the number of static ranging/imaging systems, theplacement of the static ranging/imaging systems, and the fields of viewof each static ranging/imaging system can be chosen to obtain a majorityof, if not the entirety of, a 360 degree field of view of theenvironment surrounding the vehicle. Accordingly, each staticranging/imaging system 4002 a-d can be designed to have a field of viewof approximately 90 degrees so that when all four systems 4020 a-d areimplemented, a substantial majority of a 360 degree field of view aroundvehicle 4005 can be observed. In embodiments where each staticranging/imaging system 4002 a-d has less than a 90 degree field of view,such as a 45 degree field of view, one or more additional staticranging/imaging systems can be implemented so as to extend the field ofview to achieve a combined field of view greater than that of a singlestatic ranging/imaging system.

FIG. 42 is a simplified top-down illustration of an exemplary staticranging/imaging system 4200 that includes more than one set of emissionand detection systems to achieve an expanded field of view, according tosome embodiments of the present disclosure. As shown in FIG. 42, staticranging/imaging system 4200 can include sets of emission and detectionsystems 4202 a-i mounted on a central support structure 4204, where eachset of emission and detection systems includes a respective lightemission system, e.g., light transmission system 1510 of FIG. 15, andlight detection system, e.g. light detection system 1540 of FIG. 15.Each set can be arranged radially outward from the center of supportstructure 4204 and the sets be positioned side-by-side so that theirfields of view can abut one another to form a combined field of view4206 that is a multitude times larger than a field of view for anysingle set of emission and detection systems alone. The multipleemission detection systems may all be synchronized and controlled by acommon LIDAR controller such that the end user interacts with whatappears to be a single system. In addition, the individual emissiondetection systems may all be aligned to a fixed pixel grid so that thedata simulate a wider field of view, higher resolution system operatingon a fixed field of view grid.

FIG. 43 illustrates a block diagram of an exemplary staticranging/imaging system 4300 according to some embodiments of the presentdisclosure. Static ranging/imaging system 4300 can include a lightranging/imaging device 4302 and a user interface 4350. Lightranging/imaging device 4302 can include a ranging/imaging systemcontroller 4304, a light transmission (Tx) module 4306 and a lightsensing (Rx) module 4308. Ranging data can be generated by lightranging/imaging device 4302 by transmitting one or more light pulses4310 from the light transmission module 4306 to objects in a field ofview surrounding light ranging/imaging device 4302. Reflected portions4312 of the transmitted light are then detected by light sensing module4308 after some delay time. Based on the delay time, the distance to thereflecting surface can be determined. Other ranging methods can beemployed as well, e.g. continuous wave, photodemodulation, Doppler, andthe like. Spectral image data can be generated by light ranging/imagingdevice 4302 by operating ambient-light sensor channels included insensor array 4308 in a photon-counting mode.

Light transmission module 4306 includes an emitter array 4314, which canbe a one-dimensional or two-dimensional array of emitters, and a Txoptical system 4316, which when taken together with emitter array 4314can form a light emission system 4338 similar to light transmissionsystem 1510 of FIG. 15. Tx module 4306 can further include an optionalprocessor 4318 and memory 4320, although in some embodiments thesecomputing resources can be incorporated into ranging/imaging systemcontroller 4304. In some embodiments, a pulse coding technique can beused, e.g., Barker codes and the like. In such cases, memory 4320 canstore pulse-codes that indicate when light should be transmitted. Insome embodiments, the pulse-codes are stored as a sequence of integersstored in memory.

Light sensing module 4308 can include a sensor array 4326, which can be,e.g., any of the 2D multispectral sensor arrays described above, such assensor array 600 or sensor array 900.

In some embodiments, light ranging/imaging device 4302 can be operatedin an electronic scanning mode, in which at least a LIDAR image of ascene is captured by activating only a subset of emitters at a time andby reading out only a corresponding subset of LIDAR sensor channelssimultaneous with the firing of the emitters. Different subsets ofemitters can be activated at different times with corresponding subsetsof LIDAR channels being read out simultaneously; all emitters can beeventually activated and all the LIDAR channels in the sensor array canbe read out through one emission cycle. As an example, an emitter arraycan emit light by activating one column at a time and in sequentialorder from left to right for each emission cycle while the sensor arraycan be configured to read out the corresponding LIDAR channels in acorresponding sequence. Ambient light channels can be read outsynchronously with the LIDAR channels corresponding to the samemultispectral pixels or in some other manner (e.g., all ambient-lightchannels can be read out at the same time).

To facilitate electronic scanning, some embodiments of staticranging/imaging systems can include one or more components tosynchronize the emitting and sensing of light. In some embodiments,light detection system 4336 can include a sensor controller 4325 coupledto sensor array 4326 and configured to control the operation of sensorarray 4326. Sensor controller 4325 can be any suitable component orgroup of components capable of selecting one or more photosensors tosense light, such as an ASIC, microcontroller, FPGA, or any othersuitable processor coupled to a selecting circuit, e.g., a multiplexer.Likewise, light emission system 4338 can include an emitter controller4315 coupled to emitter array 4314 and configured to control theoperation of sensor array 4326. Emitter controller 4315 can also be anysuitable processor mentioned above for sensor controller 4325 andinclude one or more driving components for operating emitter array 4314.

In some embodiments, sensor controller 4325 and emitter controller 4315are synchronized such that the sequence of light emissions in emitterarray 4314 are synchronized with the sequence of reading outphotosensors (for all sensor types or just the LIDAR channels) in sensorarray 4326. As an example, both sensor controller 4325 and emittercontroller 4315 can be coupled to a clock 4317 so that both controllerscan operate based on the same timing scheme. Clock 4317 can be anelectrical component that generates a specific signal that oscillatesbetween a high and low state at a certain speed for coordinating actionsof digital circuits. Optionally, sensor controller 4325 and emittercontroller 4315 can include their own clock circuits for coordinatingtheir own actions. In such embodiments, sensor controller 4325 andemitter controller 4315 can be communicatively coupled together via acommunication line 4319 such that sensor controller 4325 can synchronizeits clock with emitter controller 4315. That way, sensor controller 4325and emitter controller 4315 can operate sensor array 4326 and emitterarray 4314, respectively, in synchronization to effectuate imagecapture.

In some further embodiments, instead of, or in addition to, sensorcontroller 4325 and emitter controller 4315, ranging/imaging systemcontroller 4304 can be configured to synchronize the operation of lightsensing module 4308 and light transmission module 4306 such that thesequence of light emissions by emitter array 4314 are synchronized withthe sequence of sensing light by sensor array 4326. For instance,ranging/imaging system controller 4304 can instruct emitter array 4314of light transmission module 4306 to emit light by activating one columnat a time and in sequential order from left to right for each emissioncycle, and correspondingly instruct sensor array 4326 in light sensingmodule 4308 to sense light one column at a time and in the samesequential order. In such embodiments, ranging/imaging system controller4304 can have its own clock signal on which it bases its sequencinginstructions to light sensing module 4308 and light transmission module4306. It is to be appreciated that other forms of sequencing for lightdetection are envisioned and that such sequences are not limiting.Further, the collection of (intensity) data for ambient-light sensorchannels for a given multispectral pixel can be but need not be timed tocoincide with operation of the LIDAR sensor channel for thatmultispectral pixel.

Light ranging/imaging system 4300 can also include other components,which can be similar to corresponding components in FIG. 32. Signalprocessing by processor 4322 and memory 4324 can be similar toprocessing operations described above with reference to FIG. 32. Userinterface 4350 and operations thereof can be similar to the userinterface described above with reference to FIG. 32. Further, any of theranging/imaging systems described herein can interact with other systems(e.g., a vehicle control unit) rather than directly (or indirectly) witha user; such systems can control operations of the ranging/imagingsystem by exchanging appropriate control instructions, data, or othersignals with ranging/imaging system controller 4304.

3.5. Operation of Static Ranging/Imaging System

As described above, imaging operations with static ranging/imagingsystem 4300 can be performed in various modes. In one mode, referred toas “full frame” mode, all sensor channels in the array (or all sensorchannels of a given type) can be operated concurrently. In another mode,referred to as “electronic scanning” mode, different subsets of channelsmay be operated at different times. For example, as described above, Txmodule 4306 can be operated to emit light that is reflected ontodifferent portions of the sensor array in Rx module 4308 at differenttimes, e.g., by activating different emitters within Tx module 4306 orby using the same emitters in combination with MEMS-based beam steeringcomponents (e.g., MEMS mirror galvanometers, sometimes referred to as“galvos”) to control the direction of the emitted light. Differentsubsets of the LIDAR sensor channels can be selectively activated whenlight is being aimed (e.g., by selective emission and/or steering)toward those channels.

Particular ambient-light sensor channels (or particular ambient-lightphotosensors in multispectral or hybrid sensor channels) can also beoperated in either full-frame or electronic scanning modes. Infull-frame mode, all ambient-light sensor channels can be activated atthe same time, or sensor channels of different types can be activated atdifferent times. In electronic scanning mode, different subsets ofambient-light sensor channels corresponding to different areas withinthe sensor array can be activated at different times. For instance, theambient-light sensor channels corresponding to a particular group ofmultispectral pixels may be activated when the corresponding subset ofLIDAR sensor channels is activated, or the ambient-light sensor channelscorresponding to a particular group of multispectral pixels may beactivated at a time when the corresponding subset of LIDAR sensorchannels is not active.

In some embodiments, the operating mode for LIDAR and/or ambient-lightsensor channels may be selectable. Further, the LIDAR and ambient-lightsensor channels can be operated in different modes. For instance, theLIDAR channels may operate in an electronic scanning mode while theambient-light sensor channels are operated in full-frame mode to captureone spectral image for each scanning period.

In any of these and other operating modes, data can be gathered for eachsensor type for each multispectral pixel in the sensor array. Bufferingcan be used to collect data from different channels or sensor types thatcorrespond to the same multispectral pixel. Thus, as with the rotatingranging/imaging systems described above, an image comprising a set ofmultispectral image pixels across a field of view can be obtained.

4. Processing of Multispectral Images

As described above, both rotating and static ranging/imaging systems canproduce multispectral images of a field of view. A multispectral imagecan include an array of multispectral image pixels (which can be arectilinear array) and can include, for each image pixel, depthinformation extracted from one or more LIDAR sensor channels as well asinformation extracted from ambient light sensors, such as intensityvalues for various bands within the light spectrum (including visible,infrared and ultraviolet light), intensity of polarization-filteredlight, and/or other measurements as described above. Multispectralimaging provides a rich data set for a given location within a regionbeing imaged. For instance, for sensor array 400 of FIG. 4, the data setfor a given image pixel can include: distance to the imaged object(i.e., any object that happens to be visible in the particular directionassociated with the image pixel), color characteristics of the imagedobject across the visible and near-IR spectrum (e.g., intensity oramount of light collected within different wavelength bands),polarization characteristics, and absorption characteristics. Othercombinations of per-pixel image data are also possible, depending on theparticular combination of sensor channel types included in the sensorarray.

By way of example, FIG. 44 shows an example of multispectral image datathat can be acquired for a region 4402, using any of the rotating orstatic multispectral ranging/imaging systems described above (or othersimilar systems). Image group 4402 includes spectral images acquired atdifferent wavelength bands. Image group 4404 includes polarizationimages (intensity of light having a particular polarization direction).Image group 4406 represents depth images based on data provided by theLIDAR sensor channels.

The images in image groups 4402, 4404, 4406 can be inherently registeredwith each other, due to the fixed spatial arrangement of the differentsensor types. In the case of sensor arrays in rotating ranging/imagingsystems, the array can be arranged and operated such that all of thesensors in a given row image the same area in turn (e.g., as describedabove), providing trivial (or inherent) registration. In the case of 2Dmultispectral sensor arrays in static ranging/imaging systems, the imagepixel can be defined based on the area occupied by each group of sensorsof different types. For instance, in sensor array 600 of FIG. 6, eachhybrid sensor channel 602 can correspond to an image pixel, and insensor array 900, each multispectral pixel 1020 (shown in FIG. 10) cancorrespond to an image pixel. In these examples, different sensor typesmay sample different locations within the multispectral image pixel dueto (small) spatial offsets between the sensors. In some embodiments,this offset can be ignored, and the data can be treated as if allsensors were located at the center of the image pixel. Alternatively,offset compensation can be applied if desired, e.g., by interpolatingfrom nearby sensor locations to the geometric center of each imagepixel.

In some embodiments, the sensor-array ASIC can stream pixel data toanother system component (or another device) as it is acquired, and allimage processing can be performed by the other system component. Inother embodiments, the sensor array ASIC can include an “onboard” databuffer capable of accumulating data for different image pixels(including a single channel per pixel or multiple channels per pixel).Depending on implementation the onboard data buffer can hold data forany number of multispectral image pixels, from just one or two pixels upto the full image size. The buffered pixel data can be used toreconstruct a “local image” of the scene (which may be a 1D or 2D imageand may be smaller than the full image size), and the processor in thesensor array ASIC or external to the sensor array can perform variousimage processing operations on the local image, including both per-pixelanalysis and local or full scene inference. The size of the onboard databuffer can be varied as desired, depending on how much data isaccumulated and what functionality is desired. Thus, image processingand image analysis operations can be performed on-chip or off-chip asdesired.

In some embodiments, multispectral image analysis can include trainingan automated classifier using machine learning algorithms and a trainingset of images that include known (and labeled) objects. The machinelearning algorithms can include artificial neural networks or otherclassifiers (e.g., classifiers based on classical statisticaltechniques). Once trained, one or more automated classifiers can bedeployed either within the sensor array ASIC (e.g., in amachine-learning coprocessor) or in a client system that receives datafrom the sensor array ASIC.

A variety of image-processing and image-analysis operations can beperformed on a multispectral image. Examples will now be described.

4.1. Per-Pixel Analysis of Multispectral Image Pixels

In some embodiments, a rich per-image-pixel data set can enablesophisticated analysis, such as identifying materials in an image. Byway of illustration, FIG. 45 shows an example of an image that has beenannotated to identify materials contained therein. In some instances,different materials may have similar color to a human eye (e.g., a greencar and a green bush), but the materials may have subtly differentspectral signatures, different polarization characteristics and/orabsorption signatures that make them distinguishable based onper-image-pixel analysis. Combining spectral response information frommultiple ambient-light channels (including any absorption-band channels)with the depth channel data can enable classification of hard, soft, anddiffuse objects such as rock, plants, asphalt, metal, glass, water,skin, fur, clothing, and various gases and particulates like methane,carbon dioxide, black carbon, etc. Multispectral pixel information couldalso be used to classify different narrow and broad spectrum lightsources to provide other environmental cues, such as what type ofillumination is present based on spectral patterns of the pixels. Suchclassification can be performed per-pixel and in real time. In someembodiments, an artificial neural network or other machine-learningsystem (which can be implemented on-sensor or off-sensor as desired) canbe trained to classify materials from multispectral image data based ona combination of depth characteristics, color characteristics,polarization characteristics, and/or absorption characteristics;hand-annotated images can be used as training input. Once trained, themachine-learning system can make real-time identifications of what typesof objects are present in the environment and where.

As another example, real time polarimetric imaging can occur in thesensor processor and may combine data from a plurality of polarizationchannels to calculate the polarization angle and/or the degree ofpolarization. Polarimetry can be used, for instance, to provide realtime glare removal on vehicle windshields or water surfaces, to enhancecontrast in shadowed regions, to enhance imaging in the presence of hazeor other atmospheric obscurants, and/or to provide real timeidentification and classification of water, ice, and other polarizingsubstances in the environment or more specifically on the road surface.

4.2. System for Scene Inference from Multispectral Images

In some embodiments, scene-level inferences can be extracted byanalyzing the multispectral image data across a set of image pixels,which can include anywhere from two pixels to the entire image field ofview. Scene-level inference can be performed on-chip, using an onboarddata buffer in the sensor ASIC, and/or off-chip, e.g., in another systemcomponent or separate device. Many types of scene-level inferences canbe implemented.

For example, identification of distinct objects in a field of view canbe based on identifying changes in color, polarization, and/or distance.In some embodiments, results of a per-pixel analysis of likely materialcomposition can be used to identify objects based in part on the likelymaterial composition. Objects can be further assessed to determinedistance, composition, and the like. Combined with the depth informationfrom the multispectral pixels, this can provide reliable identificationof what is in the image (e.g., a car, a wall, a bush, a roadway) andwhere. It is contemplated that machine-learning systems may be enabledto determine with high reliability what types of objects are present inthe environment and where, based on multispectral image data (includingdepth data) acquired using ranging/imaging systems of the kind describedherein. Such information has a variety of uses and applications,including but not limited to driver-assistance and/or autonomous-vehicletechnology.

Other inferences can also be made. For example, in some instances, thesun or the moon may be identifiable as objects in the field of view.Using multispectral image data, the sun and the moon can be identifiedand distinguished from each other, which may provide cues as to time ofday and/or general illumination conditions. Even if the sun or moon isnot in the field of view, the different spectral properties of differentlight sources may provide cues as to whether the ambient illumination isdominated by natural sunlight (indicative of daytime hours or outdoorconditions) versus artificial illumination (indicative of night orindoor conditions such as a tunnel or parking garage). As anotherexample, the xenon-based or LED headlights of modern cars can bedistinguished from sodium-vapor streetlights. As yet another example,LED-based traffic signals emit relatively narrow (˜50 nm) spectra ofred, yellow, or green, and these spectra can be distinguished frombroader spectra of objects such as stop signs, green grass, or yellowlane lines.

5. Additional Embodiments

While the invention has been described with reference to specificembodiments, those skilled in the art with access to the presentdisclosure will appreciate that numerous variations and modificationsare possible. For instance, multispectral sensor arrays of the kinddescribed herein can be fabricated to include any number of rows and anynumber of sensor channels per row. (The terms “row” and “column” areused to distinguish two dimensions of a sensor array, particularly inthe context of arrays used in scanning mode, and are not intended toimply any particular spatial orientation of the array.) The particularconstruction of sensor channels, including channel-specificmicro-optical elements can be varied. The combination of ambient-lightsensing channels used in each row can be modified as desired, and insome embodiments different rows may have different combinations ofambient-light sensing channels. Further, the ambient light-sensingchannels are not limited to the specific examples given above; othertypes of optical filters can be used to create a variety ofambient-light sensing channels that can be used to collect image data.

The term “ambient-light sensing channel” is used herein to indicate thata sensor channel measures light intensity (as opposed to timing or otherranging data). Such channels may provide useful data in the absence ofintentional illumination emitted from the senor system. However, thisdoes not preclude intentional illumination of a field of view. Forinstance, a white light may be directed toward the field of view (e.g.,from a car's headlights or camera flash). As another example, inapplications using absorption channels, light having wavelengthsencompassing the absorption band can be directed toward the field ofview, and absence of light in the absorption channel can indicate that asubstance in the field is absorbing the light.

In addition to ambient-light sensing channel(s), a sensor arraydescribed above may include one or more LIDAR sensor channels (and/orother depth-sensing channels) that providing timing data (e.g.,histograms as described above) or other data usable to derive distancesto objects in the field of view. LIDAR sensor channels can operate atvarious wavelengths, including near infrared, shortwave infrared (e.g.,1600 nm), midwave infrared, and/or longwave infrared (e.g., up to 15μm). Further, in some embodiments additional sensor channels (e.g.,LIDAR sensor channels) can be included at locations between sensor rows,or there may be some sensor rows that do not include a LIDAR sensorchannel (or other depth-sensing channel), and images from differentsensor channels (or sensor types) can but need not have the sameresolution. Multispectral arrays can be row-based (or “1D”) arraysoperable in a scanning mode to image a field of view, or they can be 2Darrays with multispectral sensor channels or multispectral pixels.

Sensor arrays of the kind described herein can be incorporated into avariety of sensing systems, including but not limited to combinedimaging/LIDAR systems as described above. Combined imaging/LIDAR systemscan be implemented using rotating and/or static platforms as describedabove and can be used in any application where it is desirable toconcurrently collect ambient-light and ranging data.

Systems described herein can produce multispectral image data that caninclude both light intensity data for various portions of the lightspectrum (including visible, infrared, and ultraviolet with wide and/ornarrow passbands as desired; light having various polarization states;and other examples described above) and depth information across a fieldof view (which can be as wide as desired, up to 360 degrees in someembodiments). Images captured by different sensor types (includingranging sensors such as LIDAR) can be inherently registered with eachother as a result of the alignment of different sensor types on a sensorarray. In some embodiments, this inherent registration can facilitatethe generation of multispectral pixel data for an image.

Multispectral image data can be analyzed using a variety ofcomputer-implemented algorithms operating on any portion of the data. Insome embodiments, the multispectral image data can be used to generateimages for display to a user, which can include directly rendering theimage data and/or rendering an image of a scene (or portions thereof)based on algorithmic inferences from the data. While examples describedabove relate to vehicle navigation and/or driver assistance, theinvention is not limited to any particular data analysis or to anyparticular application of multispectral image data.

The above description of exemplary embodiments of the invention has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdescribed, and many modifications and variations are possible in lightof the teaching above. The embodiments were chosen and described inorder to explain the principles of the invention and its practicalapplications to thereby enable others skilled in the art to us theinvention in various embodiments and with various modifications as aresuited to the particular use contemplated. Thus, although the inventionhas been described with reference to specific embodiments, the inventionshould be understood as being limited only by the following claims.

What is claimed is:
 1. A LIDAR transmitter device comprising: an emitter array having a plurality of emitter channels arranged to emit light through a corresponding plurality of apertures in an aperture plane; a bulk optic module disposed in front of the emitter array and configured to direct light from the aperture plane into a field of view; and a plurality of channel-specific micro-optic elements, each channel-specific micro-optic element being disposed in front of a different one of the apertures and having an optical prescription that is different for different channel-specific micro-optic elements.
 2. The LIDAR transmitter device of claim 1 wherein the optical prescription for a particular one of the channel-specific micro-optic elements is based at least in part on an optical property of the bulk optic module.
 3. The LIDAR transmitter device of claim 1 wherein the bulk optic module has a curved focal plane and wherein the optical prescription of each of the channel-specific micro-optic elements compensates for an offset between a location of the aperture and a corresponding location on the curved focal plane.
 4. The LIDAR transmitter device of claim 1 wherein the optical prescription of each channel-specific micro-optic element is a function of a radial distance in the aperture plane from an optical axis of the bulk optic module to the corresponding aperture.
 5. The LIDAR transmitter device of claim 1 wherein the channel-specific micro-optic elements disposed in front of different apertures have optical prescriptions with different focusing powers.
 6. The LIDAR transmitter device of claim 1 wherein the channel-specific micro-optic elements disposed in front of different channels have different standoff distances from the aperture plane. 